I think that reusing the ComptimePtrLoad infrastructure is ultimately
less logic and more robust than adding a `direct` flag to elem_ptr.

 * Some code in zirTypeInfo needed to be fixed to create proper
   Type/Value encodings.
 * comptime elemVal works by constructing an elem_ptr Value and then
   using the already existing pointerDeref function.

There are some remaining calls to Value.elemValue which should be
considered code smells at this point.