3. implement Readonly<T>

Readonly<T> returns a type that sets all properties of T to readonly.

Pleaes implement MyReadonly<T> by yourself.

type Foo = {  a: string}const a:Foo = {  a: 'BFE.dev',}a.a = 'bigfrontend.dev'// OKconst b:MyReadonly<Foo> = {  a: 'BFE.dev'}b.a = 'bigfrontend.dev'// Error