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

[Jan Svoboda via cfe-commits]

jansvoboda11 wrote:

I'd like for @vsapsai to chime in.

As an alternative approach: could we turn these into member variables, make them non-atomic and take care to update the stats of the superior `FileManager` whenever an inferior `FileManager` goes out of scope? (e.g. after implicitly building a module)

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