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:
type Test = { id: '1' }
type Result = AppendToObject<Test, 'value', 4> // expected to be { id: '1', value: 4 }
import type { Equal, Expect } from '@type-challenges/utils'
type test1 = {
key: 'cat'
value: 'green'
}
type testExpect1 = {
key: 'cat'
value: 'green'
home: boolean
}
type test2 = {
key: 'dog' | undefined
value: 'white'
sun: true
}
type testExpect2 = {
key: 'dog' | undefined
value: 'white'
sun: true
home: 1
}
type test3 = {
key: 'cow'
value: 'yellow'
sun: false
}
type testExpect3 = {
key: 'cow'
value: 'yellow'
sun: false
moon: false | undefined
}
type cases = [
Expect<Equal<AppendToObject<test1, 'home', boolean>, testExpect1>>,
Expect<Equal<AppendToObject<test2, 'home', 1>, testExpect2>>,
Expect<Equal<AppendToObject<test3, 'moon', false | undefined>, testExpect3>>,
]