wayland: Roundtrip until we've receive initial input and output configuration

wayland: Roundtrip until we've receive initial input and output configuration

We use a ref-count mechanism to track whether parts of the init sequence
still needs round trips to receive remaining initial state.  Typically
we need a couple of roundtrips total to get the global list, then the
input and output configurations, but with the ref-count we avoid making
global assumptions like that.

https://bugzilla.gnome.org/show_bug.cgi?id=696340