codegen: Fix connect/disconnect of dynamic signals
codegen: Fix connect/disconnect of dynamic signals

Make dynamic wrapper function return handler id for later
disconnect.

https://bugzilla.gnome.org/show_bug.cgi?id=705461

flobrosch/vala-fixes,GNOME/vala,xdave/pvala,GNOME/vala,frida/vala,rvu95/vala,frida/vala,frida/vala,GNOME/vala,Distrotech/vala,spidermonkdust/vala,Distrotech/vala,rvu95/vala,GNOME/vala,spidermonkdust/vala,Distrotech/vala,flobrosch/vala-fixes,spidermonkdust/vala,frida/vala,rvu95/vala,frida/vala,flobrosch/vala-fixes