Classify iosswitch headers as private (#58405)

Summary:
Pull Request resolved: #58405

Classify the Apple Fabric Switch C++ headers as private API. Strict API consumers now receive a hard error when including these implementation headers, while React Native builds continue to use them under RN_BUILDING.

Propagate the cxxstableapi dependency from the iosswitch Buck target so its exported guarded headers resolve PrivateGuard.h.

Changelog: [Internal]

Reviewed By: cortinico

Differential Revision: D119171908

fbshipit-source-id: ba935899a990c52c243c6b1a6e80da3b7e1940f9

Author: coado

packages/react-native/ReactCommon/react/renderer/components/switch/iosswitch/react/renderer/components/switch/AppleSwitchComponentDescriptor.h

@@ -7,6 +7,8 @@
 
 #pragma once
 
+#include <react/cxxstableapi/PrivateGuard.h>
+
 #include "AppleSwitchShadowNode.h"
 
 #include <react/renderer/core/ConcreteComponentDescriptor.h>

packages/react-native/ReactCommon/react/renderer/components/switch/iosswitch/react/renderer/components/switch/AppleSwitchShadowNode.h

@@ -7,6 +7,8 @@
 
 #pragma once
 
+#include <react/cxxstableapi/PrivateGuard.h>
+
 #include <react/renderer/components/FBReactNativeSpec/EventEmitters.h>
 #include <react/renderer/components/FBReactNativeSpec/Props.h>
 #include <react/renderer/components/view/ConcreteViewShadowNode.h>