ES2015 class serialization follow-ups

The initial functionality of ES2015 classes was merged in https://github.com/facebook/prepack/pull/1176. However, there are still some outstanding areas of functionality that need addressing. These test cases are as follows:

1. Handling of computed methods

class Foo {
  bar() {
  }
}
Foo.prototype['foo bar'] = Foo.prototype.bar;
delete Foo.prototype.bar;
window.Foo = Foo;

Expected output:

class Foo {
  ['foo bar']() {
  }
}
window.Foo = Foo;

2. Ensuring additional static methods aren't serialized with the class

This should work, but we need more tests around it.

class Foo extends Bar {}
Foo.bar = function() {};
window.Foo = Foo;

Expected output:

class Foo extends Bar {}
Foo.bar = function() {};
window.Foo = Foo;

3. Ensuring prototype prorprties are handled properly when deleted

class Foo {
  bar() {
  }
  baz() {
  }
}
Foo.prototype.bar = Foo.prototype.bar.bind({});
var baz = Foo.prototype.baz;
delete Foo.prototype.baz;
var result = { Foo, baz };
window.result = result;

Expected output:

TODO

class Bar {
  bar() {
  }
}
class Foo extends Bar {
  bar() {
    super();
  }
}
window.result = {
  bar: Foo.prototype.bar
};
delete Foo.prototype.bar;

Expected Output:

TODO

4. Deletion of the constructor

class Foo { }
delete Foo.prototype.constructor;
window.Foo = Foo;

Expected Output:

TODO

class Foo {}
result = new Foo();
Foo.prototype = {};
window.Foo = Foo;

Expected Output:

TODO

class Foo { };
var result = Object.create({ constructor: Foo });
window.result = result;

Expected Output:

TODO

5. Handling of static initializers

class Foo {
  bar() {
  }
}
var x = new Foo();
x.bar.taggedFunction = cycle;
window.x = x;

Expected Output:

TODO

class Foo {
  bar() {
  }
}
var result = {
  Foo,
  bar: new Foo().bar
};
window.Foo = result;

Expected Output:

TODO

Each of these issues/cases can be dealt with as separate PRs.