feat: Allow getting inner PathBuf from SafePathBuf (#14908)

* Allow getting inner PathBuf from SafePathBuf

SafePathBuf implements AsRef<Path> which is ergonomic and useful.
However, some APIs take owned PathBufs. This leads to clunky code where
the caller has to get a &Path from the SafePathBuf then take ownership
of that path. Ideally, if a user has a SafePathBuf and needs a PathBuf,
they won't need to allocate again just to get the inner PathBuf back.

* Apply suggestion from @Legend-Master