Add outline to the bubble bar background view.

Added outline to the bubble bar background. Updated pointer
appearing/disappearing animation - now pointer moves into the bubble
bar background.
Demo: http://recall/-/gx8ASgewUeUS3QYohfrd1J/e1wZMrFZTILq73ik8wwrwx

Fixes: 345489039
Flag: ACONFIG com.android.wm.shell.enable_bubble_bar DEVELOPMENT
Test: Manual. Expand and collapse bubble bar with the light and the
dark theme.

Change-Id: I095fdc12337955aa21ee0eb622a924ad424ef186