Append to object

by Andrey Krasovsky @bre30kra69cs

实现一个为接口添加一个新字段的类型。该类型接收三个参数，返回带有新字段的接口类型。例如: ```ts type Test = { id: '1' } type Result = AppendToObject // expected to be { id: '1', value: 4 } ```