Add support for add_missing_assignments transform

[kermorgant]

Before and After

<?php

class AcmeBlogTest extends TestCase
{
    public function setUp()
    {
        $this->blog = new Blog();
    }
}

Becomes:

<?php

class AcmeBlogTest extends TestCase
{
    /**
     * @var Blog
     */
    private $blog;

    public function setUp()
    {
        $this->blog = new Blog();
    }
}

[kermorgant]

Hi @zonuexe
This is a small thing so I merge it directly in develop.

[zonuexe]

@kermorgant Thanks!