[overlay] Nest CallKit enum types within their associated classes (#4312)

Addresses the <rdar://problem/27553337>

Author: moiseev

apinotes/CallKit.apinotes

@@ -14,3 +14,9 @@ Tags:
   NSErrorDomain: CXErrorDomainRequestTransaction
 - Name: CXErrorCodeCallDirectoryManagerError
   NSErrorDomain: CXErrorDomainCallDirectoryManager
+- Name: CXCallDirectoryEnabledStatus
+  SwiftName: CXCallDirectoryManager.EnabledStatus
+- Name: CXPlayDTMFCallActionType
+  SwiftName: CXPlayDTMFCallAction.ActionType
+- Name: CXHandleType
+  SwiftName: CXHandle.HandleType

stdlib/public/SDK/CallKit/CXProviderConfiguration.swift

@@ -16,10 +16,10 @@ import Foundation
 @available(iOS 10.0, *)
 extension CXProviderConfiguration {
   @nonobjc
-  public final var supportedHandleTypes: Set<CXHandleType> {
+  public final var supportedHandleTypes: Set<CXHandle.HandleType> {
     get {
       return Set(__supportedHandleTypes.map {
-        CXHandleType(rawValue: $0.intValue)!
+        CXHandle.HandleType(rawValue: $0.intValue)!
       })
     }
     set {