[Magnifier-40] Always child of main window

Previously, we were making the magnifier surface a child of the main
window unless the magnified view was a SurfaceView, in which case we
were setting the SurfaceView to be the parent of the magnifier. In
Chrome, where the magnified views are usually SurfaceViews, this caused
the magnifier to be displayed underneath the omnibox, which was a
terrible user experience when trying to magnify the first lines of text
on a page. This was because the omnibox had a higher Z than the
SurfaceView, and therefore a higher Z than all children of the
SurfaceView (including the magnifier).

This CL sets the parent of the magnifier surface to be the main window's
surface when the magnified view is a SurfaceView as well. Therefore, the
magnifier becomes a sibling of the Chrome omnibox and, by giving the
magnifier a higher Z, it ends up being rendered on top.

Bug: 77926365
Test: atest CtsWidgetTestCases:android.widget.cts.MagnifierTest
Change-Id: Ic5b5f6ca687db8b5d842f0ab20eac70f1fd2f85e