SystemUI: handle hiding recents search bar dynamically

If the "Show recents search bar" is toggled inside Settings, we need to
catch that and reload the header bar as needed. Otherwise, having the
setting disabled would still include search bar bounds while the view
was hidden, causing some jarring animation jumps.

Ref: CYNGNOS-342

Change-Id: I74597d6d225af0395da6cb7a611bd230fc9e0675
Signed-off-by: Roman Birg <roman@cyngn.com>