Dyno: fix iterator type methods

[DanilaFe]

Closes https://github.com/Cray/chapel-private/issues/6923.

Depends on #26454, #26455 and #26456 because this causes more Domain methods to be resolved.

The issue was in resolving code like this:

class C {
  var x: int;
  var y: string;

  iter type myIter() {
    yield 3;
    yield 5;
    yield 7;
    yield 11;
  }
}

for i in C.myIter() do
  writeln(i);

Previously, dyno incorrectly set isMethod to be false, which made the this formal for methods to be incorrectly set. This PR adjusts this behavior to correctly track method calls when resolving iterator overloads.

Reviewed by @benharsh -- thanks!

Testing

• dyno tests
• paratest