In `PerformActionHelper`, use the unqualified type for lookup.
In `PerformInstanceBinding`, propagate qualifiers to the unbound element
type's class type when doing the `ConvertToValueOrRefOfType` conversion,
and to the element type when forming the `ClassElementAccess` instr
(except for `partial`, which is only used if the member being accessed
is `base`).
In handle_operator.cpp, prevent assignment to a reference to a const
type.
