Add a BC way to access environment operators/expression parsers

Hi @fabpot

Twig-CS-Fixer use his own Lexer because

• he needs to keep space/tabs
• he uses more token types

The implementation worked fine so far, but just got recently broke by the 3.21 release since I inspired my getOperatorRegex implementation by yours https://github.com/twigphp/Twig/blob/3468920399451a384bef53cf7996965f7cd40183/src/Lexer.php#L547-L551 and now getUnaryOperator/getBinaryOperator methods was removed. Of course it was possible since it's internal.

I implemented a fix to follow your new implementation https://github.com/twigphp/Twig/blob/b54a265712a475da0aef560e184d68a9affd3ace/src/Lexer.php#L528-L530 (but with some changes since I need to keep the same type for (, [, =>, ... for BC reason). But again getExpressionParsers is internal.

Is there a way to write

$expressionParsers = ['='];
foreach ($this->env->getExpressionParsers() as $expressionParser) {
     $expressionParsers = array_merge($expressionParsers, [$expressionParser->getName()], $expressionParser->getAliases());
}

without an internal method ? Would it be OK to make getExpressionParsers part of the API ?

Thanks

Start with src/Lexer.php, especially the current operator-regex implementation and getExpressionParsers, then compare the BC requirements described by Twig-CS-Fixer. Done means providing a supported way for external consumers to access the needed expression-parser or operator information without relying on internal methods.