Proposal: Add MapByElement function on slice type

[xixiwang12138]

when use lo.Map, we never use the second param，so we do need this function to improve our code

func MapByElement[T,R any](s []T, f func(T)R) []R {
	return lo.Map(s, func(t T, _ int) R {
		return f(t)
	})
}