For example when toolbars showed a menu for actions that no longer fit
(e.g. open diff viewer, reduce window size until the synchronize and
switch view buttons vanish).

Use the application flag to disable icons in menus on macOS globally
instead of doing that individually on the actions.

Change-Id: I3b682f48ee0e866f0f0d5bb0834690937f427d7f
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>