[skip ci] fix[getInternalInstanceHandleFromPublicInstance]: make it backwards compatible with previous Fabric implementation

Summary:
Changelog: [Internal]

Currently, OSS versions ofReactFabric and ReactNativeRenderer artifacts are ~2 years behind the FB version.

Fabric host components store internal instance in __internalInstanceHandle field,  previously they have been storing it in the field with the same name, but with one underscore in prefix:
https://www.internalfb.com/code/fbsource/[79c52d10beb6]/xplat/js/react-native-github/packages/react-native/Libraries/Renderer/implementations/ReactFabric-dev.js?lines=5151

Once these artifacts will be synced, the implementation will use __internalInstanceHandle field, so we can safely remove the branch with a single underscore prefix.

Differential Revision: D52697886

Author: hoxyq

packages/react-native/Libraries/ReactNative/ReactFabricPublicInstance/ReactFabricPublicInstance.js

@@ -88,5 +88,11 @@ export function getNodeFromPublicInstance(
 export function getInternalInstanceHandleFromPublicInstance(
   publicInstance: ReactFabricHostComponent | ReactNativeElement,
 ): InternalInstanceHandle {
-  return publicInstance.__internalInstanceHandle;
+  if (publicInstance.__internalInstanceHandle != null) {
+    return publicInstance.__internalInstanceHandle;
+  }
+
+  // TODO(T174762768): Remove this once OSS versions of renderers will be synced.
+  // $FlowExpectedError[prop-missing] Keeping this for backwards-compatibility with the renderers versions in open source.
+  return publicInstance._internalInstanceHandle;
 }