If ParseStructureLikeDIE (or ParseEnum) encountered a declaration DIE,
it would call FindDefinitionTypeForDIE. This returned a fully formed
type, which it achieved by recursing back into ParseStructureLikeDIE
with the definition DIE.

This obscured the control flow and caused us to repeat some work (e.g.
the UniqueDWARFASTTypeMap lookup), but it mostly worked until we tried
to delay the definition search in #90663. After this patch, the two
ParseStructureLikeDIE calls were no longer recursive, but rather the
second call happened as a part of the CompleteType() call. This opened
the door to inconsistencies, as the second ParseStructureLikeDIE call
was not aware it was called to process a definition die for an existing
type.

To make that possible, this patch removes the recusive type resolution
from this function, and leaves just the "find definition die"
functionality. After finding the definition DIE, we just go back to the
original ParseStructureLikeDIE call, and have it finish the parsing
process with the new DIE.

While this patch is motivated by the work on delaying the definition
searching, I believe it is also useful on its own.

This patch adds support for the new foreign type unit support in
.debug_names. Features include:
- don't manually index foreign TUs if we have info for them
- only use the type unit entries that match the .dwo files when we have
a .dwp file
- fix type unit lookups for .dwo files
- fix crashers that happen due to PeekDIEName() using wrong offsets where an entry had DW_IDX_comp_unit and DW_IDX_type_unit entries and when we had no type unit support, it would cause us to think it was a normal DIE in .debug_info from the main executable.

---------

Co-authored-by: paperchalice <liujunchang97@outlook.com>

and two follow-up commits. The reason is the crash we've discovered when
processing -gsimple-template-names binaries. I'm committing a minimal
reproducer as a separate patch.

This reverts the following commits:
- 51dd4eaaa29683c16151f5168e7f8645acbd6e6c (#92328)
- 3d9d48523977af3590f7dd0edfd258454cb9e9cf (#93839)
- afe6ab7586f7078cc410f6162bd9851e48e2a286 (#94400)

DWARFDebugInfo doesn't know how to resolve the "file_index" component of
a DIERef. This patch removes GetUnit (in favor of existing
GetUnitContainingDIEOffset) and changes GetDIE to take only the
components it actually uses.

This reapplies
https://github.com/llvm/llvm-project/commit/9a7262c2601874e5aa64c5db19746770212d4b44
(#90663) and added https://github.com/llvm/llvm-project/pull/91808 as a
fix.

It was causing tests on macos to fail because
`SymbolFileDWARF::GetForwardDeclCompilerTypeToDIE` returned the map
owned by this symol file. When there were two symbol files, two
different maps were created for caching from compiler type to DIE even
if they are for the same module. The solution is to do the same as
`SymbolFileDWARF::GetUniqueDWARFASTTypeMap`: inquery
SymbolFileDWARFDebugMap first to get the shared underlying SymbolFile so
the map is shared among multiple SymbolFileDWARF.

This removes `m_forward_decl_die_to_compiler_type` which is a map from
`const DWARFDebugInfoEntry *` to `lldb::opaque_compiler_type_t`. This
map is currently used in `DWARFASTParserClang::ParseEnum` and
`DWARFASTParserClang::ParseStructureLikeDIE` to avoid creating duplicate
CompilerType for the specific DIE. But before entering these two
functions in `DWARFASTParserClang::ParseTypeFromDWARF`, we already
checked with `SymbolFileDWARF::GetDIEToType()` if we have a Type created
from this DIE to avoid trying to parse the same DIE twice. So, this map
is unnecessary and not useful.

Updates:

- The previous patch changed the default behavior to not load dwos in
`DWARFUnit`
~~`SymbolFileDWARFDwo *GetDwoSymbolFile(bool load_all_debug_info =
false);`~~
`SymbolFileDWARFDwo *GetDwoSymbolFile(bool load_all_debug_info = true);`
- This broke some lldb-shell tests (see
https://green.lab.llvm.org/green/view/LLDB/job/as-lldb-cmake/16273/)
- TestDebugInfoSize.py
- with symbol on-demand, by default statistics dump only reports
skeleton debug info size
- `statistics dump -f` will load all dwos. debug info = skeleton debug
info + all dwo debug info

Currently running `statistics dump` will trigger lldb to load debug info
that's not yet loaded (eg. dwo files). Resulted in a delay in the
command return, which, can be interrupting.

This patch also added a new option `--load-all-debug-info` asking
statistics to dump all possible debug info, which will force loading all
debug info available if not yet loaded.

This reverts commit 21ddd7ff2b166c5e133b460b1a09ee8adb786ccd because it
breaks a bunch of tests:

https://lab.llvm.org/buildbot/#/builders/68/builds/69018
https://green.lab.llvm.org/green/view/LLDB/job/as-lldb-cmake/16273

Currently running `statistics dump` will trigger lldb to load debug info
that's not yet loaded (eg. dwo files). Resulted in a delay in the
command return, which, can be interrupting.

This patch also added a new option `--load-all-debug-info` asking
statistics to dump all possible debug info, which will force loading all
debug info available if not yet loaded.

When using split DWARF with .dwp files we had an issue where sometimes
the DWO file within the .dwp file would be parsed _before_ the skeleton
compile unit. The DWO file expects to be able to always be able to get a
link back to the skeleton compile unit. Prior to this fix, the only time
the skeleton compile unit backlink would get set, was if the unit
headers for the main executable have been parsed _and_ if the unit DIE
was parsed in that DWARFUnit. This patch ensures that we can always get
the skeleton compile unit for a DWO file by adding a function:

```
DWARFCompileUnit *DWARFUnit::GetSkeletonUnit();
```

Prior to this fix DWARFUnit had some unsafe accessors that were used to
store two different things:

```
  void *DWARFUnit::GetUserData() const;
  void DWARFUnit::SetUserData(void *d);
```

This was used by SymbolFileDWARF to cache the `lldb_private::CompileUnit
*` for a SymbolFileDWARF and was also used to store the `DWARFUnit *`
for SymbolFileDWARFDwo. This patch clears up this unsafe usage by adding
two separate accessors and ivars for this:
```
lldb_private::CompileUnit *DWARFUnit::GetLLDBCompUnit() const { return m_lldb_cu; }
void DWARFUnit::SetLLDBCompUnit(lldb_private::CompileUnit *cu) { m_lldb_cu = cu; }
DWARFCompileUnit *DWARFUnit::GetSkeletonUnit();
void DWARFUnit::SetSkeletonUnit(DWARFUnit *skeleton_unit);
```
This will stop anyone from calling `void *DWARFUnit::GetUserData()
const;` and casting the value to an incorrect value.

A crash could occur in `SymbolFileDWARF::GetCompUnitForDWARFCompUnit()`
when the `non_dwo_cu`, which is a backlink to the skeleton compile unit,
was not set and was NULL. There is an assert() in the code, and then the
code just will kill the program if the assert isn't enabled because the
code looked like:
```
  if (dwarf_cu.IsDWOUnit()) {
    DWARFCompileUnit *non_dwo_cu =
        static_cast<DWARFCompileUnit *>(dwarf_cu.GetUserData());
    assert(non_dwo_cu);
    return non_dwo_cu->GetSymbolFileDWARF().GetCompUnitForDWARFCompUnit(
        *non_dwo_cu);
  }
```
This is now fixed by calling the `DWARFUnit::GetSkeletonUnit()` which
will correctly always get the skeleton compile uint for a DWO file
regardless of if the skeleton unit headers have been parse or if the
skeleton unit DIE wasn't parsed yet.

To implement the ability to get the skeleton compile units, I added code
the DWARFDebugInfo.cpp/.h that make a map of DWO ID -> skeleton
DWARFUnit * that gets filled in for DWARF5 when the unit headers are
parsed. The `DWARFUnit::GetSkeletonUnit()` will end up parsing the unit
headers of the main executable to fill in this map if it already hasn't
been done. For DWARF4 and earlier we maintain a separate map that gets
filled in only for any DWARF4 compile units that have a DW_AT_dwo_id or
DW_AT_gnu_dwo_id attributes. This is more expensive, so this is done
lazily and in a thread safe manor. This allows us to be as efficient as
possible when using DWARF5 and also be backward compatible with DWARF4 +
split DWARF.

There was also an issue that stopped type lookups from succeeding in
`DWARFDIE SymbolFileDWARF::GetDIE(const DIERef &die_ref)` where it
directly was accessing the `m_dwp_symfile` ivar without calling the
accessor function that could end up needing to locate and load the .dwp
file. This was fixed by calling the
`SymbolFileDWARF::GetDwpSymbolFile()` accessor to ensure we always get a
valid value back if we can find the .dwp file. Prior to this fix it was
down which APIs were called and if any APIs were called that loaded the
.dwp file, it worked fine, but it might not if no APIs were called that
did cause it to get loaded.

When we have valid debug info indexes and when the lldb index cache was
enabled, this would cause this issue to show up more often.

I modified an existing test case to test that all of this works
correctly and doesn't crash.