xwayland: honor initially maximized requests via _NET_WM_STATE
X11 clients may request to be initially fullscreen or maximized by
setting hints in the _NET_WM_STATE property. For some reason, we are
currently only honoring fullscreen requests but not maximize.
The fixes issues with GTK apps (notably Firefox, but others as well)
not starting maximized.
There is a remaining issue that the window position may not be set
correctly after unmaximizing. This will be fixed in a follow-up commit.