cmake.lang: clean up the "operator" and "constant" contexts
cmake.lang: clean up the "operator" and "constant" contexts

CACHE and BOOL are clearly not constants, but they _are_ keywords used
by the set command, so move them to "operator". Several boolean constants
recognized by the if command are missing from "constant", so add them.

https://bugzilla.gnome.org/show_bug.cgi?id=790345

GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview