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.
This fixes a source of many compiler warnings regarding comparing the
enum VARIANT_TYPE to Variant::Type. This changes the local value to a
static const Variant::Type value rather than an unrelated enum, this
also saves us a cast.
- 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.
