message OutputRequest

What to set a screen to.

The whole state rather than the one field that changed, so that applying it is one commit: a screen asked to change mode and position in two calls would be re-laid-out twice, and the intermediate arrangement is one the user never asked for.

width/height of 0 means "the mode it prefers", refresh of 0 means "the fastest at that size", and scale of 0 means "leave it alone" — the same three defaults the config file has.