Restore corner radius for freeform tasks after recents transition

Use the finish transaction from start() or merge() to restore the corner
radius of freeform windows at the end of the recents transition.

Bug: 378657004
Flag: com.android.window.flags.enable_desktop_recents_transitions_corners_bugfix
Test: manual
Change-Id: I9b32df365237ffc25593bfa78bfc3e61fd3c4d0c