Fix popup window calculation for multi-window

If ignoreBottomDecorations=true, the display size was extracted from
the resources. However, this didn't work if the parent window was in
multi-window, as all the calculations went wrong. Instead, introduce
View.getWindowDisplayFrame which returns the "full" frame of the task
the window is currently in, without any insets, and use that to
calculate the bottom edge.

Bug: 26255254
Change-Id: I8b235b335775022ae399ee082d1200aa76cc047c