[Move-only-types] Break cycle with OpaqueReadOwnershipRequest and @objc selector
The interface-type computation in OpaqueReadOwnershipRequest is causing
a cycle with `@objc` names for the getter/setter of a property. Break
the cycle by relying on the fact that `@objc` names can only be
directly on the getter/setter, not on some other accessor, so we can
go through `getAccessor` for both cases.
I am not convinced that we won't have additional issues related to the
interface-type computation in OpaqueReadOwnershipRequest, but I
couldn't see any obvious ones in the code base either.
Fixes rdar://106575164.