Review uses of std::filesystem::path in non-filesystem contexts

Related to #8138.

The following discussion from !4925 (merged) should be addressed:

• @Assumeru started a discussion: (+8 comments)

  I realize this has nothing much to do with what this MR is trying to do, but surely this should return a VFS path?

Compressed BSAs appear to use std::filesystem::path as a means of normalizing BSA paths (which are nominally VFS paths except they're not utf-8. See also #8599 (closed).)

There might be other, similar cases that should be addressed.