Rework migration of animate_physical_bones to compatibility

doc/classes/PhysicalBone3D.xml

@@ -5,6 +5,7 @@
 	</brief_description>
 	<description>
 		The [PhysicalBone3D] node is a physics body that can be used to make bones in a [Skeleton3D] react to physics.
+		[b]Note:[/b] In order to detect physical bones with raycasts, the [member SkeletonModifier3D.active] property of the parent [PhysicalBoneSimulator3D] must be [code]true[/code] and the [Skeleton3D]'s bone must be assigned to [PhysicalBone3D] correctly; it means that [method get_bone_id] should return a valid id ([code]&gt;= 0[/code]).
 	</description>
 	<tutorials>
 	</tutorials>