Update bubble expanded view drag zones

1. Move the bottom split drag zone up over the dismiss zone
2. Offset the desktop window drag zone from the center of the screen
   (checked with UX -- this isn't centered to ensure the split zone is
   large enough)

Flag: com.android.wm.shell.enable_bubble_bar
Fixes: 416092942
Test: DragZoneFactoryScreenshotTest

Change-Id: I59023b655063147dd5ffe740b89431e79d297277