Remove FloatingTaskController & replace usages with Bubbles

Switch to using newly exposed method Bubbles#showAppBubble as what
FloatingTaskController does is no longer POR.

Calling this allows 1 bubble from a specific app to be added to the
stack. The only user of this method is NoteTaskController which is guarded by the NOTE_TASK.

Bug: 237678727
Test: treehugger
Change-Id: I47c5c010a050796eff848ba3fcabc40cf5fbd902