4. implement Record<K, V>

Record<K, V> returns an object type with keys of K and values of V.

Please implement MyRecord<K, V> by yourself.

Notice that property key could only be number | string | symbol.

type Key = 'a' | 'b' | 'c'

const a: Record<Key, string> = {
  a: 'BFE.dev',
  b: 'BFE.dev',
  c: 'BFE.dev'
}
a.a = 'bigfrontend.dev' // OK
a.b = 123 // Error
a.d = 'BFE.dev' // Error

type Foo = MyRecord<{a: string}, string> // Error