1/ Add onStartTransition() callback for SYSUI_STATE_ONE_HANDED_ACTIVE

Previously in launcher quick steps, when one handed mode trigger
the gesture is easy to conflict "swipe up Recents" and
"swipe horizontal for quick switch", we only consume gesture when
SYSUI_STATE_ONE_HANDED_ACTIVE=true, however, user have a bad
experience when one handed transitioning conflict to "swipe up
to launch recents".

Legacy design :
  onStartFinished() : SYSUI_STATE_ONE_HANDED_ACTIVE -> true
  onStopFinished()  : SYSUI_STATE_ONE_HANDED_ACTIVE -> false

New design :
  onTransition()    : SYSUI_STATE_ONE_HANDED_ACTIVE -> true
  onStartFinished() : SYSUI_STATE_ONE_HANDED_ACTIVE -> true
  onStopFinished()  : SYSUI_STATE_ONE_HANDED_ACTIVE -> false

Test: atest WMShellUnitTests
Bug: 177978035
Change-Id: Iac9612b2eb07606712a4ab3eb036ac6fd3d12ae3