Add workaround for new back flow with legacy recents animation

- Override the callback to inject back as we do today while in Overview.
  We can't rely on the client side compat callback because the Launcher
  window is not focused in this current state.

Bug: 223750399
Test: Open overview, swipe back
Change-Id: I1978ce3a91cba3e57c0f8bab366691b48a9d5921