write_demangled_name supports libc++ + clang-cl

[FatihBAKIR]

The current implementation assumes whenever we're on an FMT_MSC_VERSION compiler, the standard library is MSVC's STL. However, with clang-cl we have the possibility of using LLVM libc++ instead of MSVC STL. In that scenario, the previous implementation produced the wrong demangled names for RTTI types.

This patch detects the different combinations, and combines the existing demangling implementations to produce the correct names and make all tests pass on libc++ + clang-cl.

Fixes #4542

[FatihBAKIR]

@vitaut the lint/format_code task is failing but it also points out a file I did not touch. I also formatted the files locally with clang-format using the .clang-format file in the repo, but it still complains in CI. What's the procedure here? Should I manually apply what the CI wants including the unrelated file?

[vitaut]

The formatting issue in chrono.h has been fixed in #4557. Please rebase and it should go away.

[vitaut]

As for the formatting issue in std.h, it might be caused by a different version of clang-format. I suggest applying the change from CI manually:

-auto normalize_msvc_abi_name(string_view abi_name_view,
-                             OutputIt out) -> OutputIt {
+auto normalize_msvc_abi_name(string_view abi_name_view, OutputIt out)
+    -> OutputIt {