Show nav bar on secondary displays regardless of

... that TaskBar shows on the default display

Test: `atest MultiDisplaySystemDecorationTests` on large screen devices
Test: manual: simulate secondarydisplay + force desktop mode and check
      if nav bar shows on simulated display.
Bug: 205496049
Change-Id: I1736fbfd0f77a9fd3f07dd2fc725d99b397141c6