[js] Metadata is set after __init__

```haxe
@foo class Test {
static function __init__()
trace(haxe.rtti.Meta.getType(Test)); // {}
static function main() {
trace("Haxe is great!");
}
}
```

That's because the generated JavaScript will look like this:

```js
console.log("tests/Test.hx:3:",haxe_rtti_Meta.getType(Test));
Test.__meta__ = { obj : { foo : null}};
```

Since runtime metadata may online contain constants, it should be safe to initialize all of it before all `__init__` calls.