Record with more keys should be assignable to Record with less keys if type is a subset of the first one

[jdeniau]

import { RecordOf } from 'immutable';

export type Id = {};

type A = RecordOf<{ id: Id, param: boolean  }>;
type B = RecordOf<{ id: Id}>;

const a: A = null as any;
const b: B = a;

errors with

Type 'A' is not assignable to type 'B'.
  Type 'A' is not assignable to type 'Record<{ id: Id; }>'.
    Types of property 'has' are incompatible.
      Type '(key: string) => key is "id" | "param"' is not assignable to type '(key: string) => key is "id"'.
        Type predicate 'key is "id" | "param"' is not assignable to 'key is "id"'.
          Type '"id" | "param"' is not assignable to type '"id"'.
            Type '"param"' is not assignable to type '"id"'.

Originally posted by @thatsmydoing in #1930 (comment)

This should work as it does work with plain objects as B is a subset of A: https://www.typescriptlang.org/play?#code/KYDwDg9gTgLgBDAnmYcCSATOBeOBvOANwC44BnGKASwDsBzOAXwG4AoVpFOAQR3zioZSmADRwwAQygSAtqQBGECABtgEmnCYdkqAEJ8Cg4VkbsAxhBoU4E0r1yGh-EnADkARldMxk6XIRQAK6oLKwWVvDypPq4EsxAA