[suggestion] @:forward.op for abstracts

https://try.haxe.org/#f89E633f
```hx
class Test {
static function main() {
var x = Example.a * 5;
trace(x);
}
}

enum abstract Example(Float) to Float {
var a = 0;
var b = 1;
}
```

The above results in:
> [ERROR] Test.hx:3: characters 11-20
> 3 | var x = Example.a * 5;
> | ^^^^^^^^^
> Example should be Int

something like this crops up often where the solution is to do `var x = (Example.a:Float) * 5;` or write the @:op's for the abstract

It would be nice if we could have a `@:forward.op` meta which in this particular situation would remove the need to have the `to Float` in a lot of cases

Start by running the linked try.haxe.org example and confirming the abstract member access error. Investigate the compiler entry points for abstract forwarding and @:op metadata; done means defining the proposed @:forward.op behavior and making the example compile without explicit casts or repeated operators.

Written by the indexing model from the issue text.