Move floating rotation button handling to Launcher

Moves handling of floating rotation button when navigation
bar is not created to the launcher. This button was not
showing when taskbar is visible as it was initialized in
navigation bar (which is not created for large screens).

Bug: 200103245
Test: rotate phone when autorotate disabled on inner screen
Test: showing rotate suggestion when gesture nav enabled/disabled
Change-Id: I13dd555bcd811f1524be7ab9ad51b2b012b3b749