Add support for PHP 7's context sensitive lexer.
Summary:
This adds support for the context sensitive lexer introduced
in PHP 7 according to https://wiki.php.net/rfc/context_sensitive_lexer.
The actual list of allowed tokens was taken from PHP's master
branch on github (from https://github.com/php/php-src/blob/master/Zend/zend_language_parser.y)
Reviewers: mwolff
Reviewed By: mwolff
Subscribers: mwolff, kdevelop-devel
Differential Revision: https://phabricator.kde.org/D9380