[8.4] Add support for asymmetric visibility modifiers

Represented using new PRIVATE_SET, PROTECTED_SET and PUBLIC_SET
bits in Modifiers.

RFC: https://wiki.php.net/rfc/asymmetric

[8.4] Add support for asymmetric visibility modifiers

Represented using new PRIVATE_SET, PROTECTED_SET and PUBLIC_SET
bits in Modifiers.

RFC: https://wiki.php.net/rfc/asymmetric-visibility-v2

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Adjust tests to be compatible with PHPUnit 10 (#998)

This avoids warnings on PHPUnit 10, without actually
switching to PHPUnit 10.

Add missing void return types (#997)

Add isPublic() etc methods on Param node

Also isPromoted() to check for any flags.

Add isReadonly on Param node