Extensions: move the wheel_manager out of the extensions add-on

Move wheel management to a generic private module, prepare addon_utils
to handle changes to repositories on load (needed to resolve #123645).

tools/check_source/check_mypy_config.py

@@ -14,6 +14,9 @@ PATHS: Tuple[Tuple[str, Tuple[Any, ...], Dict[str, str]], ...] = (
     ("build_files/utils/", (), {'MYPYPATH': "modules"}),
     ("doc/manpage/blender.1.py", (), {}),
     ("release/datafiles/", (), {}),
+    ("scripts/modules/_bpy_internal/extensions/junction_module.py", (), {}),
+    ("scripts/modules/_bpy_internal/extensions/wheel_manager.py", (), {}),
+    ("scripts/modules/_bpy_internal/freedesktop.py", (), {}),
     ("tools/check_blender_release/", (), {}),
     ("tools/check_docs/", (), {}),
     ("tools/check_source/", (), {'MYPYPATH': "modules"}),