(DWARFv5) split units have an extra `dwo_id` field in the header. Type
units have `type_signature` and `type_offset`.

This commit brings support for debug_names in DWARFYAML. It parses YAML
and generates emits a DWARF5 Accelerator table with the following
limitations:

1. All forms must have a fixed length (zero length is also ok).
2. Hard-coded support for DWARF 5 and DWARF32.
3. The generated table does not contain a hash index

All of these limitations can be lifted in the future, but for now this
is good enough to enable testing.

Replace references to `enumerate` results with either const lvalue
rerences or structured bindings. I did not use structured bindings
everywhere as it wasn't clear to me it would improve readability.

This is in preparation to the switch to `zip` semantics which won't
support non-const lvalue reference to elements:
https://reviews.llvm.org/D144503.

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D145987

This reverts commit 1b589f4d4db27e3fcd81fdc5abeb9407753ab790 and relands the D89463
with the fix: update `MappingTraits<FileFilter>::validate()` in ClangTidyOptions.cpp to
match the new signature (change the return type to "std::string" from "StringRef").

Original commit message:

This:

Changes the return type of MappingTraits<T>>::validate to std::string
instead of StringRef. It allows to create more complex error messages.

It introduces std::vector<std::pair<StringRef, bool>> getEntries():
a new virtual method of Section, which is the base class for all sections.
It returns names of special section specific keys (e.g. "Entries") and flags that says if them exist in a YAML.
The code in validate() uses this list of entries descriptions to generalize validation.
This approach was discussed in the D89039 thread.

Differential revision: https://reviews.llvm.org/D89463

This reverts commit b9e2b59680ad1bbfd2b9110b3ebf3d2b22cad51b.

This:
1) Changes the return type of `MappingTraits<T>>::validate` to `std::string`
instead of `StringRef`. It allows to create more complex error messages.

2) It introduces std::vector<std::pair<StringRef, bool>> getEntries():
a new virtual method of Section, which is the base class for all sections.
It returns names of special section specific keys (e.g. "Entries") and flags that
says if them exist in a YAML. The code in validate() uses this list of entries
descriptions to generalize validation.
This approach was discussed in the D89039 thread.

Differential revision: https://reviews.llvm.org/D89463

This patch makes the opcode_base and the standard_opcode_lengths fields
of the line table optional. When both of them are not specified,
yaml2obj emits them according to the line table's version.

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D88355

This patch makes the 'ExtLen' field of extended opcodes optional. We
don't need to manually calculate it in the future.

Reviewed By: jhenderson, MaskRay

Differential Revision: https://reviews.llvm.org/D88136

This patch makes the include_directories, file_names and opcodes fields
of the line table optional. This helps us simplify some tests.

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D87878