Allow getter and setter types to be unrelated

[Andrew Branch (andrewbranch)]

Fixes #43662

The one thing to note/discuss here is that to create unrelated accessors, both the getter and setter must have explicit annotations, because the setter’s type annotation will be used for an unannotated getter return type:

// Error:
const unannotatedGetter = {
  get p() {
    return 0;
//  ^^^^^^^^ Type 'number' is not assignable to type 'string'
  },
  set p(value: string) {
    // ...
  },
};

// Ok:
const bothAnnotated = {
  get p(): number {
    return 0;
  },
  set p(value: string) {
    // ...
  }
};

I think this is probably better than making it too easy to accidentally create unrelated accessor types, but perhaps it’s not obvious from the error message that unrelated accessor types are possible.

[Ryan Cavanaugh (RyanCavanaugh)]

LGTM implementation-wise; let's double-check that we want to do this at the next meeting

[Nathan Shively-Sanders (sandersn)]

[Andrew Powell (shellscape)]

Andrew Branch (@andrewbranch) which version did this land in? having trouble finding it in changelogs

[Jake Bailey (jakebailey)]

5.1