PIP: Improve PIP control row's focus change animation in Recents

This includes following changes for performance
1. Passes the key events directly between the windows instead of using
   dummy Views and OnFocusChangeListener to prevent main thread from
   handling unnecessary focus changes.
2. Limits the window size for PIP controls to reduce unnecessary draw.

Here's the test result. Test is performed with paused PIP video
1. 5 visible recents task
  Focus down: 48.14 fps -> 85.396 fps (+77.39%)
  Focus up: 24.67 fps -> 45.33 fps (+83.77%)
2. 3 visible recents task
  Focus down: 51.98 fps -> 132.72 fps (+155.34%)
  Focus up: 30.91 fps -> 53.38 fps (+72.69%)

Bug: 28042495
Change-Id: I363232176975b160e122748c9997ef4b46b73a28