Bubble bar expanded view handle menu fixes

1. Notify the menu view controller listener that the menu is visible
   at the start rather than at the end. This ensures that the task
   view is setting an obscured area so it doesn't process touches
   while the menu is animating in.

2. Set the handle menu alpha to 1 at the beginning of the expansion
   animation. As part of the switch animation, we set the alpha of
   the handle for the bubble we are switching from to 0.

Also added a unit test for BubbleBarMenuViewController

Flag: com.android.wm.shell.enable_bubble_bar
Fixes: 399153287
Fixes: 397710596
Test: atest BubbleBarMenuViewController
Test: manual
       - have 2 bubbles in the bar
       - tap on the bar to expand
       - tap on other bubble to switch
       - tap on handle menu and dismiss bubble
       - observe handle is visible in the newly selected bubble
Test: manual
       - expand bubble bar
       - tap on handle menu and quickly try to tap on an item
          - easier to test by changing the animation durations
       - observe touch is handled correctly
Change-Id: I11c170f6293b5a24534933a6c19ef64d1b2de2f7