* getOwnedFunctionIndex no longer checks if the value is actually a
   function.
 * The callsites to `intern` that I added want to avoid the `getCoerced`
   call, so I added `intern2`.
 * Adding to inferred error sets should not happen if the destination
   error set is not the inferred error set of the current Sema instance.
 * adhoc_inferred_error_set_type can be seen by the backend. Treat it
   like anyerror.