Refine getTransformationMatrix for windows in a re-parented display

Currently, the translation of the transformation matrix computed by
WindowState.getTransformationMatrix is related to its own display.
However, if the display has been re-parented, the translation might
be misplaced to the visual result. This CL makes it return the global
transformation matrix.

Bug: 129098348
Test: atest WindowStateTests
Change-Id: I38da5b84a11890bf0f4a57eb9d5b7e71bdcc16a9