vapigen: Support shared finish methods
vapigen: Support shared finish methods

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