Fix an issue where animated the bubble bar twice from bubble button

Only animate selection changed events when the bubble bar is already
expanded, this is because we delay the expanded view showing until
the bubble bar has animated & we should wait for that signal if
we're not already expanded.

Also added a check to skip the animation if we're already showing
that bubble.

Flag: com.android.wm.shell.enable_bubble_bar
Test: manual - create a bubble from a notification and observe the
               animation
             - check that switching between bubbles still works fine
Test: atest BubblesTest
Bug: 366048860
Change-Id: I3f8341eeab645057a97b1154d221580d88d79eac