Support config files with .php extension

[yguedidi]

In addition to the already supported .twig_cs and .twig_cs.dist files, I suggest to add the support for .twig_cs.php and .twig_cs.dist.php
Inspired from PHP-CS-Fixer, they already did that in PHP-CS-Fixer/PHP-CS-Fixer#5607, they also have removed the support of old names in PHP-CS-Fixer/PHP-CS-Fixer#5609

Benefits of this move are:

• IDE will automatically detect the file as being a PHP file
• the config file can be targeted in a generic way with *.php like other PHP files to be included in other CS tools like PHP-CS-Fixer, PHP_CodeSniffer, etc, no need to maintain it as a particular case

I can try to come with a PR if the idea is accepted

[localheinz]

@yguedidi

Sounds like a good improvement to me!