[Magnifier-20] Raw Surface instead of PopupWindow

Since the movement of PopupWindows is handled by the global window
manager, using one does not provide synchronization guarantees between
the window movement and its view tree rendering. In the case of the
magnifier this was producing a shaky-text effect, when the window was
moved in one frame, but the content was only updated in the following
one (although the movement and content update were issued during the
same #show operation on the UI thread).

This CL abandons the usage of a PopupWindow for the magnifier, in favour
of a raw Surface whose movement can be controlled using the deferred
transactions API. This way, we can defer the surface movement until the
frame when the updated content is rendered. The allocated magnifier
surface is slightly bigger than the magnifier content to have space for
drawing the elevation. We obtain a native elevation by using a
RenderNode to draw the content of the magnifier.

Bug: 72041926
Test: atest CtsWidgetTestCases:android.widget.cts.MagnifierTest
Change-Id: Icb8ecf48a2f528e06790db95d54575f2ae119747