Reports resizing state to WM core so that app client could apply bigger
visible bounds while resizing splits. Also moves DividerHandleView to
more generic package.
Fix: 172704238
Test: manul check divider behavior
Test: atest WMShellUnitTests
Change-Id: I1656c86de9a0b5dfe5e6da57ccc9d5f6e467843a