Fabric: Basic implementation of <View nativeId={...}>

Summary:
Trivial.
`nativeId` is meant to be used by subclasses of external inspector-like tools, so it does not have any real functionality.

Reviewed By: fkgozali

Differential Revision: D8344064

fbshipit-source-id: d86ef378cda1f7f0e9a7b4ffc09f51004ae530d2

React/Fabric/Mounting/ComponentViews/View/RCTViewComponentView.h

@@ -36,6 +36,15 @@ NS_ASSUME_NONNULL_BEGIN
  */
 @property (nonatomic, strong, nullable) UIView *contentView;
 
+/**
+ * Provides access to `nativeId` prop of the component.
+ * It might be used by subclasses (which need to refer to the view from
+ * other platform-specific external views or systems by some id) or
+ * by debugging/inspection tools.
+ * Defaults to `nil`.
+ */
+@property (nonatomic, strong, nullable) NSString *nativeId;
+
 @end
 
 NS_ASSUME_NONNULL_END

React/Fabric/Mounting/ComponentViews/View/RCTViewComponentView.mm

@@ -53,6 +53,11 @@ using namespace facebook::react;
   }
 
   // TODO: Implement all sutable non-layout <View> props.
+  // `nativeId`
+  if (oldViewProps.nativeId != newViewProps.nativeId) {
+    self.nativeId = [NSString stringWithCString:newViewProps.nativeId.c_str()
+                                       encoding:NSASCIIStringEncoding];
+  }
 }
 
 - (void)updateEventEmitter:(SharedEventEmitter)eventEmitter