Fix NPE when entering PIP from different orientation

1. handleRequest for TRANSIT_PIP will happen before the Task appeared,
so setting ENTRY_SCHEDULED in handleRequest will cause the rotation to
access the leash before Task appeared, which causes NPE.
2. We don't want to do fixed rotation launch in Core when Shell
transition is enabled. Otherwise it will stuck at waiting for continue
rotation.

TODO: handle PIP to Fullscreen rotation in Shell transition

Bug: 210965919
Test: manual test entering PIP from different orientation without NPE
Change-Id: Ie5e61a5cf05eff7a0c1adb731d5f3d8677e0f091