UI preview of selected element

Summary:
This is a prototype for view preview within Flipper for iOS (Android next).

If enabled, a preview of the selected element is rendered in the attribute inspector.

Changelog: Add view preview/snapshot for the Layout plugin on iOS.

Reviewed By: antonk52

Differential Revision: D34990372

fbshipit-source-id: 1984514fbf59041ad236008a8db10569c5fc5f94

iOS/Plugins/FlipperKitPluginUtils/FlipperKitLayoutHelpers/FlipperKitLayoutHelpers/SKNodeDescriptor.h

@@ -105,6 +105,12 @@ typedef void (^SKNodeUpdateData)(id value);
  */
 - (void)setHighlighted:(BOOL)highlighted forNode:(T)node;
 
+/**
+ Used to grab a snapshot of the specified node which is currently selected in
+ the Flipper application.
+ */
+- (UIImage*)getSnapshot:(BOOL)includeChildren forNode:(T)node;
+
 /**
  Perform hit testing on the given node. Either continue the search in
  one of the children of the node, or finish the hit testing on this

iOS/Plugins/FlipperKitPluginUtils/FlipperKitLayoutHelpers/FlipperKitLayoutHelpers/SKNodeDescriptor.mm

@@ -68,6 +68,10 @@
   return @[];
 }
 
+- (UIImage*)getSnapshot:(BOOL)includeChildren forNode:(id)node {
+  return nil;
+}
+
 - (void)setHighlighted:(BOOL)highlighted forNode:(id)node {
 }