This allows removing it from `class_db.h`, significantly reducing the amount of files
that include it transitively.
Also includes some include cleanup in `control.h` and `rich_text_label.h` done while
ensure they don't depend on `callable_mp`.
If the module is enabled (default), 2D physics works as it did before.
If the module is disabled and no other 2D physics server is registered
(via a module or GDExtension), then we fall back to a dummy
implementation which effectively disables 2D physics functionality (and
a warning is printed).
The dummy 2D physics server can also be selected explicitly, in which
case no warning is printed.
Rémi Verschelde
Thaddeus Crews
kobewi
David Snopek
Aaron Franke
funkysandwich
Yufeng Ying
Ricardo Buring
Raul Santos
smix8