Remove === and !== when using Twig >=3.23

Twig provides these operators natively now, so our own implementation is
not needed anymore.

Replace internal class used from Twig

Make library fully compatible with Twig 3.21

Merge pull request to fix incompatibility with Twig v3.21

Redefines ForeachTokenParser::parseAssignmentExpression slightly to account for new protected function of the same name.

Add ForElseNode to avoid deprecation notice in Twig 3.19+

Reduce to PHP 8 as minimum version to match twig

Add YieldReady attributes

Add missing type hints

Avoid PHP warnings for break & continue

Our previous mechanism of doing a "lookbehind" with twig
lead to array key warnings. Instead we now look ahead, which
is also valid from the perspective of twig, to determine if
more loops are ending than closing, and for break if enough
loops are ending to break out of.

Check if loop exists for continue

Otherwise the variable might not be defined and
lead to a PHP notice.