Mapped type should take a function form as well #21421

According to #12114 mapped types currently support following forms:

{ [ P in K ] : T }
{ [ P in K ] ? : T }
{ readonly [ P in K ] : T }
{ readonly [ P in K ] ? : T }

I think it shall also at least support a function form:

{ ([ P in K ]) : T }
{ ([ P in K ]) ? : T }
{ ([ P in K])(entities: P[], someBoolean: boolean) ? : T }

Currently Im trying to implement a Functionize<T> interface which forces implementors to implement any property of the T, but make it a function with maybe additional arguments. Example:

interface User {
     name: string;
     age: number
}

I want to do Functionize which I want to give me:

{
       name(names: string[]): string;
       age(ages: number[]): number;
}

And I'm asking about following method signature:

type Functionize<T> = {
   [P in keyof T](values: T[])?: T[P];
};