Ultrasound: Fix touchable region for windows on off-screen display

The ultrasound digital pen uses an external logical display, dedicated
to digital pen off-screen input. Apps using this feature use the
Android Presentation class to put Views on this display.
When calculating the touchable region for windows on this logical
display, Android uses the stack bounds of the activity, which is
placed on the main display. This yields an incorrect touchable
region for Views in the off-screen display, since the main display
and the off-screen display have different resolutions.
This fix sets the touchable region to be the entire window frame
for windows which reside in the digital pen off-screen display.

Change-Id: Ife87fc42b39a4bf75c8cfb194ae876c65e7ff4f9