Feature Request: `+` operator should join non-string types if `.toString()` method exists

[JairusSW]

Feature suggestion

I find it frustrating that both the left and right sides of a String.concat/+ operator cannot join, for example, string and i32.
In JavaScript, it

1. Checks to see if the right side of the binary expression is a string
2. If not, it then checks if the right side has a .toString(): string method
3. If so, it calls it and concatenates left + right.toString()

Would be quite simple to implement. For example, this would probably work:

export class String {
  ...
  @operator("+")
  _concat<T>(left: string, right: T): string {
    if (!isDefined(right.toString())) ERROR(...);
    return this.concat(left, right.toString());
  }
}