Adds overlay_cache_ptr to keep a disabled overlay in memory when it's expected to be shown again.
Most input_overlay_deinit calls are replaced with input_overlay_unload, which caches the overlay unless initing/deiniting core or disabling overlays.
Loading a cached overlay is done as a swap, intended for osk_toggle.
Related updates:
- Fewer parameters for the overlay loading task. Use current settings when enabling an overlay
- Add input_overlay_check_mouse_cursor() to preserve show/hide mouse behavior
- Don't apply input_overlay_show_mouse_cursor in windowed mode (controlled by mouse grab only)
- Remove some dead code
8a81d39437