Support a way to reason about a field's type from the record/class type

[bradcray]

This issue requests ways to reason about the type of a record type's field, such as:

record myRecordType {
  var myField: int;
}

…myRecordType.myField.type…

Note that this is somewhat related to issue #11816 (which is similar, but more general) and #12167 which is attractive due to the ability to get a field's type without knowing its name.

[DanilaFe]

I was a little confused at first, but I think you're requesting the following:

record R {
  var x: int;
}
type t = R.x.type;

Initially, I interpreted your request as:

record R {
  var x: int;
}
var myRecord: R;
type t = myRecord.x.type;

Which already works today.

Just commenting this for anyone else who might get confused like I did.

[bradcray]

Good point Daniel—I've updated the title and OP to try and clarify this.