Add a BinaryTreeNode example for Cxx TMs (#41767)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/41767

Changelog: [Internal]

Adds a simple example showing a direct recursive node in a Cxx TM.

Currently we can't auto-generate [the necessary C++ Types](https://reactnative.dev/docs/next/the-new-architecture/cxx-custom-types#struct-generator) - but we can add it later if this scenarios becomes really common.

Direct recursive nodes, can't be value types - it would require infinite memory. Hence they are nullable and managed by a smart pointer.

Reviewed By: rshest

Differential Revision: D51784136

fbshipit-source-id: f6f0710d03583bdf1e6e72ba42d8df7f8ff8d915

packages/rn-tester/js/examples/TurboModule/NativeCxxModuleExampleExample.js

@@ -43,6 +43,7 @@ type Examples =
   | 'getConstants'
   | 'getCustomEnum'
   | 'getCustomHostObject'
+  | 'getBinaryTreeNode'
   | 'getGraphNode'
   | 'getNumEnum'
   | 'getStrEnum'
@@ -104,6 +105,12 @@ class NativeCxxModuleExampleExample extends React.Component<{||}, State> {
       NativeCxxModuleExample?.consumeCustomHostObject(
         NativeCxxModuleExample?.getCustomHostObject(),
       ),
+    getBinaryTreeNode: () =>
+      NativeCxxModuleExample?.getBinaryTreeNode({
+        left: {value: 1},
+        value: 0,
+        right: {value: 2},
+      }),
     getGraphNode: () =>
       NativeCxxModuleExample?.getGraphNode({
         label: 'root',