Using `misc/scripts/fix_headers.py` on all Godot files.
Some missing header guards were added, and the header inclusion order
was fixed in the Bullet module.
- Now it is usable from both `CanvasItem` and `Spatial` editors.
- `EditorPlugin` API changes:
- `forward_draw_over_canvas()` becomes `forward_draw_over_viewport()`.
- `update_canvas()` becomes `update_overlays()`, which now triggers the update of every overlay on top of any 2D or 3D viewports present. Also now it returns the number of such viewports, which is useful whenever you need to know the number of draw-over calls you'll get.
- New: `[set/is]_force_draw_over_forwarding_enabled()` to force overlaying regardless it handles the current object type, in a similar fashion as `[set/is]_input_event_forwarding_always_enabled`. This kind of overlay is also on top of those for regular handled node types.
- New: `forward_force_draw_over_canvas()`, which is the callback that gets called for plugins that enable forced overlaying.
- Makes vararg methods automatically use PROPERTY_USAGE_NIL_IS_VARIANT on return types
- Completely removes the ":type" suffix for method names. Virtual methods must use the MethodInfo constructors that takes Variant::Type or PropertyHint as the first parameter for the return type (with CLASS_INFO as a helper to get the PropertyInfo). Parameters must use PROPERTY_HINT_RESOURCE_TYPE and hint string.
- PROPERTY_USAGE_NIL_IS_VARIANT is no longer needed for parameters, because parameters cannot be void.
- Adds missing PROPERTY_USAGE_NIL_IS_VARIANT to virtual and built-in methods that return Variant.
Currently we rely on some undefined behavior when Object->cast_to() gets
called with a Null pointer. This used to work fine with GCC < 6 but
newer versions of GCC remove all codepaths in which the this pointer is
Null. However, the non-static cast_to() was supposed to be null safe.
This patch makes cast_to() Null safe and removes the now redundant Null
checks where they existed.
It is explained in this article: https://www.viva64.com/en/b/0226/
