types(schema): support required: { isRequired: true } syntax in schema definition

[vkarpov15]

Re: #13514

Summary

One potential workaround for #13514 is using object syntax for defining required, because the following works fine:

new Schema({
  email: {
    type: String,
    required: { isRequired: true, message: 'Email is required' }
  }
});

But we don't currently support that in TypeScript. This PR adds support for the required: { isRequired: true } syntax. Unfortunately doesn't help very much with #13514.

Examples

[hasezoey]

Change looks good to me, but the test not really

[IslandRhythms]

LGTM