Rename bubble bar flyout fields

Long term we'd like to use bubbles for any app, so this change
uses more general names instead of the chat-specific naming

Flag: com.android.wm.shell.enable_bubble_bar
Bug: 277815200
Test: built and tested on a device
Change-Id: Idec2aa7d9a8df5df0df49231e8871298084f8aa1