Add new fullscreen mode

Add new fullscreen mode showing only the current active view in fullscreen.

The current fullscreen mode set the tabbed multi-view widget fullscreen, i.e. all views are maximized, including separators and decoration. The new mode is intended to be closer to a "classical" fullscreen mode.

This fullscreen mode is notably useful on zSpace Inspire where stereo rendering requires that view resolution perfectly match the display physical resolution. See !6688 (merged)