Do not dispatch leashes if they are not ready

The previous solution used a different transaction from the one used in
SeamlessRotator#finish. So the transaction might be applied in an
unexpected order between here and there when the target frame number is
reached.

This CL reverted the previous solution. Instead, we don't dispatch the
leash if it is not ready. For the client, it won't play the animation
until obtaining the leash.

Fix: 154195854
Test: Rotate device to change the orientation in Camera, and see if
      navigation bar stays visible.
Test: Check if transient bar can be shown/hidden/aborted as expected.
Test: Make sure b/153104643 stay fixed.
Test: atest InsetsPolicyTest
Change-Id: I29f80f1c77615b0a3cde38df265220f48d66f117