Create missing overrides bug with unary operators

[FMorschel]

Repro:

abstract class MyClass {
  bool operator -();
}

class Other extends MyClass{}

Turns into:

abstract class MyClass {
  bool operator -();
}

class Other extends MyClass{
  @override
  bool operator unary-() {
    // TODO: implement unary-
    throw UnimplementedError();
  }
}

FYI @bwilkerson

[bwilkerson]

Clearly a bug. Not sure how often users are running into it.

[FMorschel]

I don't override operators that much, and even less so unary ones, so probably not that often.