- EditorSettings: Ensure that `create()` makes a valid singleton.
Fixes#49179, fixes#49450.
- EditorPaths: Cleanup code, properly set `paths_valid`.
- EditorPaths: Move more paths validation (check, mkdir) from
EditorSettings for a better separation of concerns.
- EditorPaths: Move EditorFileSystem creation of `.godot/imported`
next to other paths.