Hide launcher when freeform tasks are visible

This CL introduces a new controller to manage the visibility of the
launcher workspace when desktop mode is active and freeform tasks
are visible.

This controller will be notified when the sysui state flag related
to freeform task visibility is changed.

The controller will modify the workspace visibility as well as
the flags on the activity indicating if it's been paused / resumed
based on freeform tasks being visible or not.

Bug: 245569277
Test: manual -  enable desktop mode and open some freeform tasks
             => observe that the contents of launcher is hidden and
                taskbar shows
             -  remove all of the freeform tasks
             => observe that the contents of launcher reappears along
                with the hotseat.
Change-Id: I378ab97b40cbb954a06f4e2426b195efddad905c