Show mounted ComponentKit views in Flipper

Summary:
Before this diff, Flipper showed *leaf* views created by ComponentKit, but not any intermediate views. Now we show both.

A new node type `SKComponentMountedView` is used for this purpose. Its descriptor `SKComponentMountedViewDescriptor` mostly delegates to its view's descriptor, but redirects back into ComponentKit for children.

Reviewed By: Andrey-Mishanin

Differential Revision: D21130997

fbshipit-source-id: b3c12ea7cc1200962b3ba7c269c48d68b1809948

iOS/Plugins/FlipperKitLayoutPlugin/FlipperKitLayoutComponentKitSupport/SKComponentMountedView.mm

@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#if FB_SONARKIT_ENABLED
+
+#import "SKComponentMountedView.h"
+
+@implementation SKComponentMountedView
+
+- (instancetype)initWithView:(UIView*)view
+                    children:(std::vector<SKComponentLayoutWrapper*>)children {
+  if (self = [super init]) {
+    _view = view;
+    _children = std::move(children);
+  }
+  return self;
+}
+
+@end
+
+#endif