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`.
- Removes `native_menu.h` dependency from `display_server.h`.
It's now forward-declared in all DisplayServer implementations and should
be included in the .cpp's.
- Removes some unused `rb_set.h` and `rb_map.h` dependencies, which leads to
having to include them explicitly in half the scene and editor codebase...
which shows how much we depend on `display_server.h`.
- Forward-declare `input_event.h`, so now we need only `keyboard.h`.
Rémi Verschelde
passivestar
A Thousand Ships
Lukas Tenbrink