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.h

@@ -0,0 +1,35 @@
+/*
+ * 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.
+ */
+
+#import <Foundation/Foundation.h>
+
+#import <vector>
+
+NS_ASSUME_NONNULL_BEGIN
+
+@class SKComponentLayoutWrapper;
+
+/**
+ Represents a non-leaf view created by ComponentKit. Its corresponding
+ descriptor CKComponentMountedViewDescriptor delegates to the view's descriptor
+ for attributes and most other behaviors, but redirects back into ComponentKit's
+ SKComponentLayoutWrapper when queried for children.
+
+ In this way, non-leaf views created by ComponentKit appear in the Flipper
+ layout hierarchy as the child of the component that created their view.
+ */
+@interface SKComponentMountedView : NSObject
+
+- (instancetype)initWithView:(UIView*)view
+                    children:(std::vector<SKComponentLayoutWrapper*>)children;
+
+@property(nonatomic, readonly) UIView* view;
+@property(nonatomic, readonly) std::vector<SKComponentLayoutWrapper*> children;
+
+@end
+
+NS_ASSUME_NONNULL_END