[Magnifier-42] Fix bug in window positioning

The position of the magnifier surface is always clamped inside its
parent surface. As of Ic5b5f6ca687db8b5d842f0ab20eac70f1fd2f85e, we are
always trying to make the magnifier surface a child of the main
application window, if possible (before, if the magnified view was a
SurfaceView, we were making the magnifier a child of the SurfaceView's
surface). However, the CL did not also update the clamping, continuing
to clamp to the SurfaceView space when the magnified view was a
SurfaceView (even if the magnifier was child of the main window). This
was making the magnifier window to be wrongly positioned on the screen
when the magnified view is a SurfaceView. The current CL fixes this.

Bug: 78876353
Test: manual testing
Test: atest CtsWidgetTestCases:android.widget.cts.MagnifierTest
Change-Id: I63f2b185f58e62e8ad6eadf788e641fb1de07b04