On X11 we won't always receive cursor positions, as some other client
might have grabbed the pointer (e.g. for implementing a popup menu). To
make screen casting show a somewhat correct cursor position, we need to
actively poll the X server about the current cursor position.
We only really want to do this when screen casting or taking a
screenshot, so add an API that forces the cursor tracker to track the
cursor position.
On the native backend this is a no-op as we by default always track the
cursor position anyway.
https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1391
