Pipe finish callback through synthetic recents path

- Launcher still relys on this callback for cleaning up after the
  transition completes

Flag: EXEMPT (unused without enableFallbackOverviewInWindow)
Bug: 366021931
Test: atest RecentsTransitionHandlerTest
Change-Id: I73ec8524e27e30d7d6f5e6bbe5269e79c3cc08e2