Unify the comment style of inline @var comments

Problem/Motivation

Inline @var comments are useful for some IDEs to provide code complete feature for developers, such as PHPStorm.

But there is no standard about it as I know -- Checked API documentation and comment standards

In Drupal and contrib modules, I saw two styles are used, starts with /** @var and /*

Proposed resolution

As it's an inline comment, I suggest using /*

Pointed by @kaysenlau according to phpDocumentor, should use /** @var

class Foo
{
  /** @var string|null Should contain a description */
  protected $description = null;
}

Remaining tasks

• Needs discussion
• Replace all comments in core following the new unified standard