"Uncaught TypeError: itf.GenericRetval is not a function" when calling a generic function via interface

```
interface IBar {
function GenericRetval Void>>():T;
}

class Test {
static function main() {
var itf:IBar = new Bar();
var fails:Foo = itf.GenericRetval(); // Uncaught TypeError: itf.GenericRetval is not a function,
trace('fails = ${fails.number}');
}
}

```
Doing the exact same thing via var obj : Bar = new Bar() works as expected.
Full test case can be found in [Test.zip](https://github.com/HaxeFoundation/haxe/files/7820508/Test.zip) and at https://try.haxe.org/#1d3F0529

**Remark:** Possibly related to JS target, I only tested this one (and spent about an hour on it) but I'm not 100% sure either.

Start with the attached Test.zip or the try.haxe.org reproduction and confirm the failure when the generic function is called through IBar on the JavaScript target. Trace the compiler's interface and generic-function handling; done means the interface call works without the TypeError while the existing direct Bar call remains working.

Written by the indexing model from the issue text.