gtk: implement -full-screen
Aiming for GTK as replacement for SDL, a feature like -full-screen should also
be implemented.
Bringing the window into full-screen mode is done by activating the "Fullscreen"
menu item. This is done after showing the windows to make the cursor and menu
hidden.
v2: drop -no-frame implementation, use booleans instead of ints and ensure
consistency between ui state and menu.
Signed-off-by: Peter Wu <[email protected]>
Reviewed-by: Anthony Liguori <[email protected]>
Signed-off-by: Michael Tokarev <[email protected]>