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

[Fangrui Song via cfe-commits]

MaskRay wrote:

(BTW: https://discourse.llvm.org/t/hidden-emails-on-github-should-we-do-something-about-it/74223 The recommendation is to avoid the github "hidden email" feature.)

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