Allow floating tasks to be shown as bubbles (behind a sysui flag)

Special "app bubble" that is ordered at the front of the list unless
something else was selected. This is guarded behind the flag to
enable floating tasks, and a new flag to allow floating tasks to be
bubbles.

Test: manual  - enable the flags and create a floating task
             => floating task appears in a bubble
Bug: 237678727
Change-Id: Ibf66e8bae07800b5f64598c9b50de7a7995d09e6