@:java.default vs. interface order

@kevinresol found a problem with #10466 which I have isolated to this case:

```haxe
extern interface I1 {
@:java.default function test():Void;
}

extern interface I2 {
function test():Void;
}

class C implements I1 implements I2 {

}

function main() {

}
```

This fails with `Field test needed by I2 is missing`. If the `implements` order of `I1` and `I2` is swapped, the error disappears. The compiler doesn't normally care about identical interface methods, so it just picks whichever it finds first.

This seems annoying to handle...