Introduce "done foo" as shortcut for "emit foo; done" (#4412)

As discussed in Raku/problem-solving#249

This makes the "done" sub a multi and adds a candidate that does an `emit` of the value, before actually doing a `done`.

src/core.c/control.pm6

@@ -197,9 +197,14 @@ sub emit(Mu \value --> Nil) {
     nqp::setextype($ex,nqp::const::CONTROL_EMIT);
     nqp::throw($ex);
 }
-sub done(--> Nil) {
+proto sub done(|) {*}
+multi sub done(--> Nil) {
     THROW-NIL(nqp::const::CONTROL_DONE);
 }
+multi sub done(Mu \value --> Nil) {
+    emit value;
+    done;
+}
 
 proto sub die(|) {*};
 multi sub die(--> Nil) {