New sniff: change nested dirname() calls to use $levels parameter

[jrfnl]

Sniff basics	-
Fixable for PHP:	7.0+
Sniff type:	Modernize
Fixer type:	Safe

Short description

PHP 7 introduced a $levels parameter for the dirname() function. Using this parameter is more efficient than having several nested calls to the dirname() function.

Related PHPCompatibility sniff(s):

• NewFunctionParameters

PHP manual references:

• 7.0.0 | Added the optional levels parameter.

  http://php.net/manual/en/function.dirname.php

Example code:

Detect the following code pattern(s):

dirname( dirname( $file ) );
dirname( dirname( dirname( dirname( __FILE__ ) ) ) );
dirname(dirname(dirname(__DIR__)));
dirname( dirname( dirname( dirname( __DIR__, 2 ) ) ) );

And fix these to:

dirname( $file, 2 );
dirname( __FILE__, 4 );
dirname(__DIR__, 3);
dirname( __DIR__, 5 );

Notes for implementation of the sniff:

• Spacing within the function call should not be changed by the sniff.
• The sniff should check for the second parameter and if it already exists, adjust it, rather than add the parameter.

Loosely related to issue #2