[Support] Add llvm::xxh3_128bits (#95863)

Add a 128-bit xxhash function, following the existing
`llvm::xxh3_64bits` and `llvm::xxHash` implementations. Previously,
48e93f57f1ee914ca29aa31bf2ccd916565a3610 added support for
`llvm::xxh3_64bits`, which closely follows the upstream implementation
at https://github.com/Cyan4973/xxHash, with simplifications from Devin
Hussey's xxhash-clean.
However, it is desirable to have a larger 128-bit hash key for use cases
such as filesystem checksums where chance of collision needs to be
negligible.

So to that end this also ports over the 128-bit xxh3_128bits as
`llvm::xxh3_128bits`.

Testing:
- Add a test based on xsum_sanity_check.c in upstream xxhash.

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