Darwin: MTRDeviceControllerFactory cleanup (#32960)

* Darwin: MTRDeviceControllerFactory cleanup

Internal methods don't need a named category
Use ivars directly (most internal properties were never used as properties)
Use MTR_DIRECT_MEMBERS for internals / implementation
No need to pre-declare internal methods used only with the same file

* Darwin: MTRDeviceControllerFactory cleanup (cont)

Reorder ivars a little to group related things

* Darwin: MTRDeviceControllerFactory cleanup (cont)

Allocate C++ objects that are created at init time directly as ivars instead of
as pointers. This avoids the need for manual cleanup code.

* Fix darwin-framework-tool link issue

* restyle

src/darwin/Framework/CHIP/MTRDeviceController.mm

@@ -551,7 +551,7 @@ - (BOOL)startup:(MTRDeviceControllerStartupParamsInternal *)startupParams
         }
 
         errorCode = chip::Credentials::SetSingleIpkEpochKey(
-            _factory.groupData, fabricIdx, _operationalCredentialsDelegate->GetIPK(), compressedId);
+            _factory.groupDataProvider, fabricIdx, _operationalCredentialsDelegate->GetIPK(), compressedId);
         if ([self checkForStartError:errorCode logMsg:kErrorIPKInit]) {
             return;
         }