[clang] [modules] Add diagnostic about performed input file validation when encounter unrecoverable changed input file. (PR #180899)

[Cyndy Ishida via cfe-commits]

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cyndyishida wrote:

Could the `FileChange` part of `err_fe_ast_file_modified` be changed to a note instead? That way, it won't show up in the IDE. The general sentiment around the `mtime changed (was 1763764800, now 1763767206)` is negative, but that information is still useful to capture. It would be better if it's just information that compiler engineers know to look for in logs. 

https://github.com/llvm/llvm-project/pull/180899