Add `BLI_change_working_dir(path)` to change the current working directory.
This change is required for adding USDZ support to Blender. When exporting to that format, we are required to do a weird change of directory because of a quirk with the USD library's USDZ functionality. If an absolute filepath is passed into the `UsdUtilsCreateNewUsdzPackage` function, the USDZ archive will store that full path.
macOS uses `NSFileManager` through some new Mac-only wrapper functions.
Ref #99807
Pull Request #104525
ceba1854f9