[clang-tools-extra] [libc++] Implement ranges::contains (PR #65148)

[Konstantin Varlamov via cfe-commits]

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var-const wrote:

Can you please go through various `robust` test files and add tests for `contains` where it makes sense? Let me know if you need any help with that!

https://github.com/llvm/llvm-project/pull/65148