[@loopback/sequelize] Nested Loopback model types are not supported

[KalleV]

Describe the bug

If you have existing Loopback model properties set up that are nesting other Loopback models such as this "Address" example:

loopback-next/packages/repository-json-schema/src/__tests__/unit/build-schema.unit.ts

Lines 478 to 518 in be0c53e

	it('allows nesting models', () => {
	@model()
	class Address {
	@property()
	street: string;
	@property()
	city: string;
	@property()
	state: string;
	}
	@model()
	class Email {
	@property()
	label: string;
	@property()
	id: string;
	}
	@model()
	class User {
	@property({id: true})
	id: string;
	@property({
	type: 'string',
	required: true,
	})
	name: string;
	@property({
	type: Address,
	})
	address?: Address;
	@property.array(Email)
	emails: Email[];
	}

it will lead to an error about unsupported types.

Logs

Example error:

Error: Unhandled DataType "class Address extends repository_1.Model {
  }" for column "address" in sequelize extension

Additional information

References:
https://loopback.io/doc/en/lb4/Model.html#json-schema-inference

Reproduction

N/A