iOS: Add very basic diagnostic screen

Summary:
Adds an extremely barebones in-app screen for showing sonar diagnostics.
The UI is laughable, but it's wired up. Leaving proper design to a later commit.

Like in the android case, state is currently passed as a string, but will become something much more structured after this is in place.

Reviewed By: priteshrnandgaonkar

Differential Revision: D9218766

fbshipit-source-id: 4889ed79b928056a67b1e8cb8a40a9bd52e084f1

iOS/SonarKit/FlipperDiagnosticsViewController.h

@@ -0,0 +1,17 @@
+/*
+ *  Copyright (c) 2018-present, Facebook, Inc.
+ *
+ *  This source code is licensed under the MIT license found in the LICENSE
+ *  file in the root directory of this source tree.
+ *
+ */
+#ifdef FB_SONARKIT_ENABLED
+
+#import <UIKit/UIKit.h>
+
+@interface FlipperDiagnosticsViewController : UIViewController
+@property(strong, nonatomic) UIScrollView *scrollView;
+@property(strong, nonatomic) UILabel *stateLabel;
+@end
+
+#endif