fix(shaker): typescript enums support (#761)

[Anber]

Motivation

Fix for #761

Summary

Enums are transpilled to functions with side effects, which shaker mistakenly drops.

enum Color {
  black = '#000'
}

to

var Color;
(function (Color) {
  Color["black"] = "#000";
})(Color || (Color = {}));

This PR changes the way how shaker evaluates dependencies of statements and expressions.

Test plan

One test was added, few tests were extended.