display: Always show refresh rate
Refresh rates are an important information for users, even if they
can't change them.
This is especially true for cases where knowledge of the refresh
rate may influence the decission about the resolution to use.
Consider the example where a display may support 3840x2160@60Hz
and 2560x1440@144Hz. When choosing 3840x2160 as resolution,
the refresh rate will likely get hidden, making the user unaware
of the fact that they will maybe not get what they want (potentially
144Hz).
So follow the example of e.g. the sound panel where input and output devices are listed in dropdowns, even if they are the only options selectable.
Note: while this is a design change, for a big group of users this won't actually change the default experience as Mutter until recently had a bug to duplicate 60Hz modes in many cases. So most laptop users already saw the refresh rate panel in previous Gnome versions, dispite it having little use.
See also: mutter@fb9564b8
P.S.: for some nice reason the panel is inactive by default (unlike for the sound devices). This makes it more pleasant to look at and (not) interact with:
Closes: #395 (closed)