Fix divider rounded corner on specific devices

On large rounded corner devices, Rounded corners around divider
cannot display right corner path because it need more space to
draw corners and divider bounds is fixed.

Fix this by enlarging the divider window bounds. However, if we only
enlarge it, it will cause divider touch region too big to make app
hard to interactive. Therefore, migrate touch region setting logic
in legacy split to here, only set divider handle view size as touch
region.

Fix: 202808282
Test: flash on barbet and active split screen to check
Test: pass existing tests
Change-Id: If292c0d4c598d75672ec821d1fee45a8892b236f