zend_ast: Wrap class names in parens during export when they are an expression

[TimWolla]

Fixes #22387.

[iliaal]

X::class (ZEND_AST_CLASS_NAME) still goes through zend_ast_export_ns_name(), so (bar)::class exports as bar::class, which re-parses to the string "bar" rather than (bar)::class. Same case as the (bar)::m() / (bar)::$p / (bar)::C ones already covered. Switching that branch to zend_ast_export_ns_name_or_expression() fixes it, and it's worth a (bar)::class line in the test.

[TimWolla]

I had seen that and then during testing it complained about ::class not being legal on a string (since I was testing with a string constant) and then disregard that as a case that cannot happen in practice. Of course AST printing also needs to work with runtime errors, and constants can contain objects.

Now fixed, thanks.

[iliaal]

LGTM