"::class resolution as scalar" Feature

FOR RFC: https://wiki.php.net/rfc/class_name_scalars

Patch addresses:
* Allows for Name::class, self::class, static::class, parent::class resolution to a scalar based on current use rules and current namespace.
* Reuses existing keyword "class"
* Alters zend_compile.c\zend_resolve_class_name() to facilitate compile time class name resolution (and runtime by way of FCALL)