C#: Replace Xform and XformInv with * operator

- In cases where both `Xform`/`XformInv` and the `*` operator were
implemented the `Xform`/`XformInv` methods were removed in favor of the
`*` operator.
- In cases where the `Xform`/`XformInv` existed but not the `*` operator,
the `Xform`/`XformInv` methods were replaced with the `*` operator.
- In cases where no method existed, a new `*` operator has been
implemented to support the same operations that are supported in GDScript.
- Fixes the `Transform.Xform` and `Transform.XformInv` with `Rect2`
implementation to use a zero `Rect2` size to start expanding from
(which is how it's implemented in C++).

modules/mono/editor/script_templates/CharacterBody3D/basic_movement.cs

@@ -26,7 +26,7 @@ public partial class _CLASS_ : _BASE_
         // Get the input direction and handle the movement/deceleration.
         // As good practice, you should replace UI actions with custom gameplay actions.
         Vector2 inputDir = Input.GetVector("ui_left", "ui_right", "ui_up", "ui_down");
-        Vector3 direction = Transform.basis.Xform(new Vector3(inputDir.x, 0, inputDir.y)).Normalized();
+        Vector3 direction = (Transform.basis * new Vector3(inputDir.x, 0, inputDir.y)).Normalized();
         if (direction != Vector3.Zero)
         {
             velocity.x = direction.x * Speed;