[JVM] Make generics work with return type in sigs (#5080)
[JVM] Make generics work with return type in sigs (#5080)

This intends to port the changes to src/vm/moar/Perl6/Ops.nqp from
https://github.com/rakudo/rakudo/pull/5048 to the JVM backend.
salortiz/rakudo,rakudo/rakudo,salortiz/rakudo,salortiz/rakudo,tbrowder/rakudo,rakudo/rakudo,salortiz/rakudo,MasterDuke17/rakudo,MasterDuke17/rakudo,MasterDuke17/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,tbrowder/rakudo,rakudo/rakudo,salortiz/rakudo,MasterDuke17/rakudo,rakudo/rakudo,rakudo/rakudo,rakudo/rakudo,tbrowder/rakudo,tbrowder/rakudo,salortiz/rakudo,tbrowder/rakudo,MasterDuke17/rakudo