[clang] [clang-tools-extra] [lldb] [llvm] [Support][JSON] Use `std::unordered_map` for object storage (PR #171230)

[Sabianin Maksim via cfe-commits]

s-mx wrote:

@zixu-w Is it possible to check perf of `StringMap` here?

https://llvm.org/docs/ProgrammersManual.html#llvm-adt-stringmap-h

https://github.com/llvm/llvm-project/pull/171230