Seems like a good first issue

It required function overloading due to Array.from has different signatures with different arity:

from<T>(arrayLike: ArrayLike<T>): T[];
from<T, U>(arrayLike: ArrayLike<T>, mapfn: (v: T, k: i32) => U, thisArg?: any): U[];

and should support also this:

Array.from({ length: 128 }) // ArrayLike interface required only "length"

I think we can at least have a subset of the functionality. It would be nice for easy cloning at least. Wdyt?

@MaxGraey This could currently be handled with defaults, except for the thisArg.

from<T, U = T>(arrayLike: ArrayLike<T>, mapfn: (v: T, k: i32) => U = (t: T, k: i32) => t): U[];