Convert BubblePositionerTest to deviceless testing

This change introduces Robolectric to WMShell and converts BubblePositionerTest
to a bivalent test.

Flag: NONE
Bug: 308004028
Test: atest BubblePositionerTest
Change-Id: I0aa7ccd99d20fadc86429615f249124eb3f4f51b
9 files changed