[DependencyScanningFilesystem] Make sure the local/shared cache filename...

[DependencyScanningFilesystem] Make sure the local/shared cache filename lookups use only absolute paths (#66122)

Previously a relative path would be used as a key for cache lookup and
if the same relative path was used from another compiler invocation with
a different working directory then the first cache entry was erroneously
returned.

(cherry picked from commit 36b37c77)