Support for IsFunction

[haejunejung]

It provides support for IsFunction.

Functions are distinct from objects, arrays, and tuples. Identifying functions separately allows you to apply function-specific logic or type handling.

For example as below.

type T0 = IsFunction<Function> // true
type T1 = IsFunction<() => void> // true
type T2 = IsFunction<(a: number, b: number) => number> // true

type T4 = IsFunction<[number]> // false
type T5 = IsFunction<{}> // false
type T6 = IsFunction<Record<any, any>> // false
type T7 = IsFunction<[]> // false