codegen: Get rid of transform_expression
codegen: Get rid of transform_expression

It was not possible to return any extra temporary variable from
transform_expression for compound types like arrays or delegates,
thus producing subtle bugs.

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