Add a short-hand for redirecting function calls

[matanlurey]

I ❤️ the fact that factory constructors accept an "=" symbol:

abstract class A {
  factory A({String a}) = _ConcreteA;
}

With the addition of optional new/const, the difference between static functions and factory constructors seems basically to be the ability to say "const" and the ability to be able to use this awesome syntax.

I'd love to be able to use this for all method invocations:

class DelegatingList<T> implements List<T> {
  void add(T item) = super.add;
}

This would also make invoking super in general so nice if allowed:

class B extends A {
  B(arg1, arg2, arg3, arg4, arg5, arg6) = super;
}

Or to use generated functions without writing lots of boilerplate:

part 'foo.g.dart';

foo(arg1, arg2, arg3, arg4) = _$foo;

[matanlurey]

I still have hope this can happen ❤️

[eernstg]

Here is a proposal that substantially overlaps this issue: dart-lang/language#3444.