Add multiline_comment_opening_closing rule

[samuelmaudo]

This PR recovers a rule to format multiline comments consistently.

With this rule, this code:

/******
 * Multiline comment with arbitrary asterisks count
 ******/

/**\
 * Multiline comment that seems a DocBlock
 */

/**
 * DocBlock with arbitrary asterisk count at the end
 **/

becomes:

/*
 * Multiline comment with arbitrary asterisks count
 */

/*\
 * Multiline comment that seems a DocBlock
 */

/**
 * DocBlock with arbitrary asterisk count at the end
 */

It was included in the PHP CS Fixer ruleset, so if we replace it by the Symfony ruleset, it might be interesting to include it in our ruleset.