Zend: Use pointer to zend_type for variance checks

[Girgias]

Depends on #18256

[DanielEScherzer]

Okay for ext/reflection

[iluuu1994]

What's the motivation behind this? Does it improve assembly size due to better argument passing? All the type macros also work on pointers, so this becomes a bit unergonomic. But I don't have big objections.

[Girgias]

Main motivation is for #18260 where I want to store a pointer to the bound zend_type in a HashTable. This might also pave the way for #18189 if we start reusing zend_types instead of copying them. Could definitely use the 32bit of padding of zend_type for a refcount field.

[iluuu1994]

IMO, the overhead of refcounting to save 8 bytes (8 byte pointer vs zend_type of size 16 bytes) is not worthwhile. Interning the complex type (i.e. the zend_type.ptr field) should be enough, and doesn't require any changes to the type struct. You could make an argument that interning the full type is cleaner, but in practice it's unlikely to make a real difference.

That said, passing types through args as pointers might still make sense, at least if they're not immediately copied to the new call frame. If the intention is to do this on a larger scale, it might make sense to introduce macros that work on pointers. Feel free to ask for other opinions.