codegen: Simplify get_*_cexpression() and split out get_cexpression()
codegen: Simplify get_*_cexpression() and split out get_cexpression()

GNOME/vala,GNOME/vala,frida/vala,GNOME/vala,frida/vala,frida/vala,frida/vala,frida/vala,GNOME/vala