Set the bubble bar background scale for initial animation

When turning off DND all the previous bubbles get reposted and
the bubble bar background scale is set for stashed state incorrectly.

This change sets the background scale correctly.

Flag: com.android.wm.shell.enable_bubble_bar
Fixes: 377597242
Test: manual
       - send some bubbles in the bubble bar
       - go to settings -> do not disturb -> turn on
       - observe bubbles are hidden
       - turn do not disturb off
       - observe bubbles animate in correctly
Change-Id: I50c07248fb95cf3ae92c86090838c40901918220