Fortran: Tolerate #include loops in dependency scanner

The function `cmFortranParser_FilePush` was always processing the
provided (included) file, even though it may have been processed before.
This lead to infinite recursion in cases where the include guards were
not properly interpreted, e.g. `# if !defined` instead of `#ifndef`.
This commit introduces a cache of paths to already processed files.
These files are now ignored in `cmFortranParser_FilePush` (treated as
non-existing).

Fixes: #27238