GValue: Move explicit cast support to separate function
GValue: Move explicit cast support to separate function

rvu95/vala,themiwi/vala,spidermonkdust/vala,playya/vala,tjol/vala-tjol,themiwi/vala,frida/vala,jessevdk/vala,Jc2k/vala,frida/vala,frida/vala,Distrotech/vala,severinh/vala,kamanashisroy/aroop,severinh/vala,frida/vala,severinh/vala,frida/vala,rvu95/vala,playya/vala,flobrosch/vala-fixes,themiwi/vala,flobrosch/vala-fixes,spidermonkdust/vala,rvu95/vala,phako/vala,GNOME/vala,Distrotech/vala,jessevdk/vala,tjol/vala-tjol,xdave/pvala,kamanashisroy/aroop,jessevdk/vala,flobrosch/vala-fixes,phako/vala,kamanashisroy/aroop,Jc2k/vala,playya/vala,GNOME/vala,spidermonkdust/vala,Distrotech/vala,GNOME/vala,GNOME/vala,tjol/vala-tjol