Refactored Node3D rotation modes

* Made the Basis euler orders indexed via enum.
* Node3D has a new rotation_order property to choose Euler rotation order.
* Node3D has also a rotation_mode property to choose between Euler, Quaternion and Basis

Exposing these modes as well as the order makes Godot a lot friendlier for animators, which can choose the best way to interpolate rotations.
The new *Basis* mode makes the (exposed) transform property obsolete, so it was removed (can still be accessed by code of course).

core/variant/binder_common.h

@@ -88,6 +88,7 @@ struct VariantCaster<const T &> {
 VARIANT_ENUM_CAST(Object::ConnectFlags);
 
 VARIANT_ENUM_CAST(Vector3::Axis);
+VARIANT_ENUM_CAST(Basis::EulerOrder);
 
 VARIANT_ENUM_CAST(Error);
 VARIANT_ENUM_CAST(Side);