[Divider] Fix wrong drag handle position for RTL layout

Fix miscalculation of the drag handle postion when secondary container
is fully expanded in RTL and BTT layout directions. Also did code clean
up during the fix.

Bug: 343307918
Test: atest DividerPresenter
Change-Id: I3036773255554567d8961a5cd8ee5cd47118aab2
3 files changed