[clang] [clang-tools-extra] [Clang] [Diagnostics] Simplify filenames that contain '..' (PR #143520)

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eaeltsin wrote:

> I can revert and then reland this if the issue is pressing for you

@Sirraide - this is pressing us, so please clean revert first. Thank you!


https://github.com/llvm/llvm-project/pull/143520