[clang] [clang][scan-deps] Add option to disable caching stat failures (PR #144000)

[Michael Spencer via cfe-commits]

Bigcheese wrote:

> LGTM. I think I would slightly prefer for `DependencyScanningWorkerFilesystem` to accept the entire service instead of its members (for the same reasons we do that in the worker, action, etc.)

I changed this, although now the tests need a service. I don't think that's a big deal as real use always has a service. It also required moving stuff out of the header as the service includes the vfs, so the service can't be a complete type in the vfs header.

https://github.com/llvm/llvm-project/pull/144000