Creates BubbleBarController

Creates BubbleBarController which is responsible for registering
a listener to hear about bubble state changes and propagates those
changes to BubbleBarViewController.

Additionally, it loads the data and creates the individual BubbleViews
that are added to BubbleBarView.

Bug: 253318833
Test: manual, with other CLs, see go/bubble-bar-tests
Flag: WM_BUBBLE_BAR
Change-Id: I45b0d3a764cd14b2fc5d34aec2b81c7fecb541cf