Cancel recents animation when touch home key

There should send an opening task transition to remote transition
handler to finish the recents animation. For now there is no opening
transition send to Shell because the exist home activity won't be
collected while start home activity.

Bug: 207297486
Test: 1. Enable shell transition.
      2. Setup 3rd-party launcher as default home.
      3. Entering Recents from home.
      4. "adb shell input keyevent KEYCODE_HOME", verify recents
	 animation will be dismissed.
Test: atest NexusLauncherTests:com.android.quickstep.FallbackRecentsTest
Change-Id: Ib3b897d97e3fdee3131556d2810b49d434e0e70a