Fix Area monitorable in 2D and 3D Godot physics.

[madmiraal]

In Godot physics (2D and 3D), when an Area's Monitorable property is changed, it updates the broadphase collision checker by changing the static field. This removes any active collision pairs and creates new ones. Currently, deleting an active collision pair will trigger area_exited signals. However, the Area's status is not changed, so the new pair is ignored until something else forces an update e.g. moving the Area.

This patch does two things, both of which are required to fix the issues with changes to Monitorable not working. First, when changing the Monitorable property, it calls _shapes_changed(), which adds the Area to the Space's moved areas' list, which will trigger a collision update for the new collision pair created. Second, it ensures that only areas that were Monitorable are added to the Areas removed list when the collision pair is deleted. This also ensures that the new pair's area_entered signals are not cancelled by the old pair's area_exited signals.

Fixes #23484
Fixes #27441

Note: This does not fix being unable to disable Monitorable in Bullet physics. This is fixed in #42306.

[pouleyKetchoupp]

This fix looks good, it just needs a rebase.

[akien-mga]

Thanks!