Plugin-php: Support php7.3 and php7.4

[alexander-akait]

No issue template. We need improve parser (https://github.com/glayzzle/php-parser):

php7.3

• [x] Support trailing commas in call/isset/unset (spec https://wiki.php.net/rfc/trailing-comma-function-calls)
• [x] Support new syntax for NowDoc and HereDoc (spec https://wiki.php.net/rfc/flexible_heredoc_nowdoc_syntaxes)
• [x] Array Destructuring supports Reference Assignments
• [x] Instanceof Operator accepts Literals (i think we already support, need add tests)

php7.4

• [x] https://wiki.php.net/rfc/null_coalesce_equal_operator
• [x] https://wiki.php.net/rfc/typed_properties_v2
• [x] https://wiki.php.net/rfc/arrow_functions_v2
• [x] https://wiki.php.net/rfc/spread_operator_for_array
• [x] https://wiki.php.net/rfc/numeric_literal_separator

Something missing? Any help welcome :+1:

[cseufert]

From the looks it closing #1346 should close this too, so does this mean that prettier should work fine for all php 7.4 features?

[czosel]

@cseufert Yes! I updated the checkboxes above accordingly. Once #1291 and #1295 landed, we have full support for PHP 7.3 and 7.4! :tada: I hope we can release this real soon :wink: