This PR is a subset of the commits made in
https://github.com/swiftlang/llvm-project/pull/10710.

The most notable change is the addition of `PrefixRange` and
`SuffixRange` which are a catch-all to track anything after or before a
function's demangled name. In the case of Swift, this allows to add
support for name highlighting without having to track the range of the
scope and specifiers of a function (this will come in another PR).

Uses the `TrackingOutputBuffer` to populate the new member `Mangled::m_demangled_info`.

`m_demangled_info` is lazily popluated by `GetDemangledInfo`. To ensure `m_demangled` and `m_demangled_info` are in-sync we clear `m_demangled_info` anytime `m_demangled` is set/cleared.

https://github.com/llvm/llvm-project/pull/131836

Add version of GetDemangledName that will force re-demangling. This is required because LLDB will SetDemangledName without going through the demangler. So we need a way to force demangling to set the m_demangled_info member when we need it.

https://github.com/llvm/llvm-project/pull/131836

The original PR is #132274.

Co-authored-by: @bulbazord Alex Langford

Reverts llvm/llvm-project#132274

Broke a test on LLDB Widows on Arm:
https://lab.llvm.org/buildbot/#/builders/141/builds/7726
```
FAIL: test_dwarf (lldbsuite.test.lldbtest.TestExternCSymbols.test_dwarf)
<...>
    self.assertTrue(self.res.Succeeded(), msg + output)

AssertionError: False is not true : Command 'expression -- foo()' did not return successfully

Error output:

error: Couldn't look up symbols:

  int foo(void)

Hint: The expression tried to call a function that is not present in the target, perhaps because it was optimized out by the compiler.
```

This patch addresses the issue #129543.
After this patch the size of lldb-server is reduced by 9MB.

Co-authored-by: @bulbazord Alex Langford

This patch refactors `Mangled::GetDemangledName` to use LLVM's preferred
early-return style. I'm planning on introducing a way to force
re-demangling of names in a future patch, and this stylisitc cleanup
makes that easier to reason about.

Also performed small cleanups where I could:
* we can handle `eManglingSchemeNone` inside the switch instead of a
separate if-block
* removed some redundant explicit StringRef<->C-string conversions

rdar://142329765

Follow up to #93881. Updates missed tests and handles `_Dmain`.

Reduce false positive identification of C names as Dlang mangled names. This happens 
when a C function uses the prefix `_D`.

The [Dlang ABI](https://dlang.org/spec/abi.html#name_mangling) shows that mangled names 
have a length immediately following the `_D` prefix. This change checks for a digit 
after the `_D` prefix, when identifying the mangling scheme of a symbol. This doesn't 
prevent false positives entirely, but does make it less likely.