Set KeyboardQuickSwitchView ratio correctly.

This CL sets the thumbnailView ratio correctly in Alt-Tab UI. The currently supported ratios are `SNAP_TO_30_70, SNAP_TO_50_50, SNAP_TO_70_30`. This can be extended when we add more split modes later.

Bug: 328691131
Test: manual in both landscape and portrait mode.
Flag: EXEMPT bugfix
Recall: http://recall/clips/79f3b250-d691-4b03-93c3-825a80478ae0

Change-Id: Idf4f174d1b222a8f3c80e5c6ed17c5bf53d3368c