Implicit cast declarations for abstracts from T

Imagine that you have such kind of code: https://try.haxe.org/#57017
Should compiler complain about implicit casting declarations for abstract where underlying type is type variable without constraints? IMO only `@:from` `@:to` declarations with explicit type transformation must be permitted for this case.

Code:
```haxe
class Test {
static function main() {
trace("Haxe is great!");
var x:MyType = 0.1;
var y:Bool = x;
trace(x, y);
}
}

abstract MyType(T) from Float from String to Int to Bool {

}
```