Bunlde ClientTransactionItems when enter/exit PiP

Enter PiP:

After this CL, PauseActivityItem, TopResumedActivityChangeItem, and
WindowStateResizeItem will be bundled.

However, ActivityConfigurationChangeItem will not.

This is because the ActivityRecord will become unfocusable when
mWaitForEnteringPinnedMode is set, and pause the PiP activity, while the
bounds and windowing mode will be updated after the enter PiP
transition.
Also, the PipStateTransactionItem will come from a separate IPC call
from WM Shell.

Exit PiP:

After this CL, ResumeActivityItem and ActivityConfigurationChangeItem
will be bundled.

Bug: 333452456
Test: manually verify enter/exit PiP
Change-Id: I462f58fc05d4bb63155bc9e1c88414e6801a66be