[clang] [clang-scan-deps] Fix contention when updating `TrackingStatistic`s in hot code paths in `FileManager`. (PR #88427)

[Alexandre Ganea via cfe-commits]

aganea wrote:

> LGTM, thanks!

Thanks for the review!

> (Out of interest, what machine are you seeing the contention with?)

It's a ThreadRipper Pro 3975WX 32c/64t running on with Windows 11.

https://github.com/llvm/llvm-project/pull/88427