[php-src] Issue #7900: `never` return type for arrow functions with throw expressions

Issue: https://github.com/php/php-src/issues/7900 Comment Author: bwoebi The general problem is that return <expr> is forbidden at compile-time (which the short closure expands to). Now, if we loosen this restriction, we have to completely get rid of the compile-time check, for short closures, and just check at runtime. (We cannot just see throw, because calling another function returning never is equally valid.)