Make platform-only scrollview implementation headers private (#58917)

Summary:
Pull Request resolved: #58917

Mark three platform-specific `react/renderer/components/scrollview` headers as private:
- iOS `RCTComponentViewHelpers.h` (previously untiered): the `RCTScrollViewProtocol` / `RCTScrollViewHandleCommand` helper used only by React Native's own iOS ScrollView component view to dispatch commands.
- Android `AndroidHorizontalScrollContentViewComponentDescriptor.h` and `AndroidHorizontalScrollContentViewShadowNode.h` (previously "for frameworks"): the component is registered only by React Native's own Android core components registry, and the shadow node is only included by its descriptor.

Changelog: [Internal]

Reviewed By: cortinico

Differential Revision: D123623731

fbshipit-source-id: 3d78d7957bb94d6880775348d3998bc2910eef26

Author: coado

packages/react-native/ReactCommon/react/renderer/components/scrollview/platform/android/react/renderer/components/scrollview/AndroidHorizontalScrollContentViewComponentDescriptor.h

@@ -7,7 +7,7 @@
 
 #pragma once
 
-#include <react/cxxstableapi/FrameworksGuard.h>
+#include <react/cxxstableapi/PrivateGuard.h>
 
 #include <React/RendererCore.h>
 #include <react/renderer/components/scrollview/AndroidHorizontalScrollContentViewShadowNode.h>

packages/react-native/ReactCommon/react/renderer/components/scrollview/platform/android/react/renderer/components/scrollview/AndroidHorizontalScrollContentViewShadowNode.h

@@ -7,7 +7,7 @@
 
 #pragma once
 
-#include <react/cxxstableapi/FrameworksGuard.h>
+#include <react/cxxstableapi/PrivateGuard.h>
 
 #include <React/RendererCore.h>
 #include <React/View.h>

packages/react-native/ReactCommon/react/renderer/components/scrollview/platform/ios/react/renderer/components/scrollview/RCTComponentViewHelpers.h

@@ -5,6 +5,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+#include <react/cxxstableapi/PrivateGuard.h>
+
 #import <Foundation/Foundation.h>
 #import <React/RCTDefines.h>
 #import <React/RCTLog.h>