This reverts commit 0fa20c55b58deb94090985a5c5ffda4d5ceb3cd1.

Storing raw symbol names is generally preferred in profile files.
Demangling might lose information. Language frontends might use
demangling schemes not supported by LLVMDemangle
(https://github.com/llvm/llvm-project/issues/45901#issuecomment-2008686663).
In addition, calling `demangle` for each function has a significant
performance overhead (#102222).

I believe that even if we decide to provide a producer-side demangling,
it would not be on by default.

Pull Request: https://github.com/llvm/llvm-project/pull/102274

FNV is slow and the name StableHashing.h might be misleading. Just use
xxh3_64bits, which has been adopted in many places.

- Add `MachineVerifierPass`.
- Use complete `MachineVerifierPass` in `VerifyInstrumentation` if
possible.

`LiveStacksAnalysis` will be added in future, all other analyses are
done.

This improves consistency in the trace files as other entries are
demangled too.
Submitted by jamieschmeiser on behalf of trass3r
@jamieschmeiser @An-DJ

Text files should be opened with OF_Text to have the correct encoding.

The patch didn't consistently clean up `#ifdef LLVM_ENABLE_ABI_BREAKING_CHECKS` and '#if defined(LLVM_ENABLE_ABI_BREAKING_CHECKS)' paths, causing a lot of build failures

`LLVM_ENABLE_ABI_BREAKING_CHECKS` is always defined:

https://github.com/llvm/llvm-project/blob/72c901f5e59477e568b1b04dae9de753b9d1f6f3/llvm/include/llvm/Config/abi-breaking.h.cmake#L16C2-L16C15
It uses `cmakedefine01` rather than `cmakedefine`, so
`LLVM_ENABLE_ABI_BREAKING_CHECKS` is always defined,
so the preprocessed code is probably not what the author wanted.

I'm planning to remove StringRef::equals in favor of
StringRef::operator==.

- StringRef::operator==/!= outnumber StringRef::equals by a factor of
  70 under llvm/ in terms of their usage.

- The elimination of StringRef::equals brings StringRef closer to
  std::string_view, which has operator== but not equals.

- S == "foo" is more readable than S.equals("foo"), especially for
  !Long.Expression.equals("str") vs Long.Expression != "str".

We need it to test isel related passes. Currently
`verifyMachineFunction` is incomplete (no LiveIntervals support), but is
enough for testing isel pass, will migrate to complete
`MachineVerifierPass` in future.

When analyzing pass debug output it is helpful to have the function name
along with the loop name.