Support changes in php 8.0 syntax? #247

The following changes may matter for the language specification in PHP 8.0 - feel free to split out separate tickets

https://wiki.php.net/rfc/named_params
https://wiki.php.net/rfc/namespaced_names_as_token
https://wiki.php.net/rfc/nullsafe_operator
https://wiki.php.net/rfc/match_expression_v2
https://wiki.php.net/rfc/non-capturing_catches
Trailing commas in parameters/closure use
https://wiki.php.net/rfc/union_types_v2
https://wiki.php.net/rfc/static_return_type
https://wiki.php.net/rfc/mixed_type_v2

Additionally, the php 8.0 attributes syntax is still being voted on