Blender Git Loki

Fix T86431: Keep memory location of the window manager on file load

Keep the pointer location from the initial window-manager
between file load operations.

This is needed as the Python API may hold references to keymaps for e.g.
which are transferred to the newly loaded window manager,
without their `PointerRNA.owner_id` fields being updated.

Since there is only ever one window manager, keep the memory at the same location so the Python ID pointers stay valid.

Reviewed By: mont29

Ref D10690