[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.

Author: DougGregor

lib/AST/Decl.cpp

@@ -6309,7 +6309,7 @@ getNameFromObjcAttribute(const ObjCAttr *attr, DeclName preferredName) {
 ObjCSelector
 AbstractStorageDecl::getObjCGetterSelector(Identifier preferredName) const {
   // If the getter has an @objc attribute with a name, use that.
-  if (auto getter = getOpaqueAccessor(AccessorKind::Get)) {
+  if (auto getter = getAccessor(AccessorKind::Get)) {
       if (auto name = getNameFromObjcAttribute(getter->getAttrs().
           getAttribute<ObjCAttr>(), preferredName))
         return *name;
@@ -6339,7 +6339,7 @@ AbstractStorageDecl::getObjCGetterSelector(Identifier preferredName) const {
 ObjCSelector
 AbstractStorageDecl::getObjCSetterSelector(Identifier preferredName) const {
   // If the setter has an @objc attribute with a name, use that.
-  auto setter = getOpaqueAccessor(AccessorKind::Set);
+  auto setter = getAccessor(AccessorKind::Set);
   auto objcAttr = setter ? setter->getAttrs().getAttribute<ObjCAttr>()
                          : nullptr;
   if (auto name = getNameFromObjcAttribute(objcAttr, DeclName(preferredName))) {

test/ClangImporter/Inputs/move_only_types_cycle.h

@@ -0,0 +1,16 @@
+#import <Foundation/NSObject.h>
+#import <Foundation/NSUUID.h>
+
+__attribute__((objc_subclassing_restricted))
+__attribute__((swift_name("TricksyClass")))
+__attribute__((external_source_symbol(language="Swift", defined_in="MyModule", generated_declaration)))
+@interface CPTricksyClass : NSObject
+
+@end
+
+@protocol P
+@property(readonly) NSUUID *uuid;
+@end
+
+@interface CPTricksyClass() <P>
+@end

test/ClangImporter/move_only_types_cycle.swift

@@ -0,0 +1,21 @@
+// RUN: %target-typecheck-verify-swift -target %target-cpu-apple-macosx10.15 -swift-version 5 -import-objc-header %S/Inputs/move_only_types_cycle.h
+// REQUIRES: objc_interop
+// REQUIRES: OS=macosx
+
+// This test triggered a cyclic dependency between @objc getter selector
+// checking and some checking for move-only types, which is both horrifying and
+// exciting at the same time.
+
+import Foundation
+
+@objc(CPTricksyClass)
+public class TricksyClass: NSObject {
+  public enum Color {
+    case red
+  }
+
+  var id = UUID()
+}
+
+extension TricksyClass.Color {
+}