Run reveal animation from relative top of window

The window frame may not align with its parent if the app
doesn't draw under the display cutout. So the shift-up reveal
animation for the app main window needs to subtract the offset
to align with its parent.

Otherwise there will be a gap between the main window and its
container, e.g. expect to animate top from 40px to 0px but
it becomes 60px to 20px, then the 20px gap may be a strange
translucent area.

Bug: 317319213
Bug: 323114927
Test: On a device with a display cutout on top.
      Launch an activity with style windowFullscreen=true and
      windowLayoutInDisplayCutoutMode=default.
      There won't have a gap between the cutout area and app
      window when playing the open animation.

Change-Id: I2ac5b0a5301af78ae26c7373d2edae4c0c0ab0f2