Use the bounds of WindowToken to compute window bounds

Previously, we use InsetsState#getDisplayFrame as the initial bounds in
computeWindowBounds. However, the frame cannot be moved by the display
area policy. This CL uses the bounds of WindowToken which can be
affected by the display area policy.

Fix: 172451212
Test: Enter one-handed mode and see if ScreenDecorOverlays are laid out
      as expected.
Change-Id: I27328f76591b805223a5b7d3e2cf14b40185816d