Fix 2D scale gizmo placement
This PR fixes the placement of the scale gizmo for 2D nodes whose pivot has been moved.
A similar issue was fixed in #25380, also by taking into account the pivot. This PR introduces a helper function to hopefully prevent the issue from occurring in other places. I wasn't sure if the helper should indicate it's returning a value which includes the pivot or not - perhaps someone with more experience with the engine can weigh in.