Fix wrong bar state after swiping home

Interrupt the animation when the user swipes home.

When there are no bubbles the stashed state now keeps getting
updated so that when a bubble is created we can correctly
detect stash change events.

Flag: com.android.wm.shell.enable_bubble_bar
Fixes: 378967270
Test: manual
       - dismiss bubble bar
       - launch app
       - send bubble
       - swipe home during the animation
       - observe the bar does not stash at the end
Change-Id: I2f054b7110af68f9637a4011a378ba35776b3771