Keep RCTHermesInstanceFactory.h off the "for frameworks" C API header (#59111)

Summary:
Pull Request resolved: #59111

`RCTHermesInstanceFactory.h` is part of React's umbrella header, so every `import React` compiles it. It imported `<react/runtime/JSRuntimeFactoryCAPI.h>`, which the C++ stable API classifies as "for frameworks", only to get the opaque `JSRuntimeFactoryRef` handle. So an app that defines `RN_STRICT_API` gets a "for frameworks" warning from React Native's own header that it cannot act on: with the prebuilt SwiftPM artifacts the warning fires while the `React` module is built with the app's macros.

Declare the handle in the header instead, the same way `RCTJSRuntimeConfiguratorProtocol.h` already does (`typedef void *JSRuntimeFactoryRef;`). The type and ABI are unchanged, and identical typedefs may be repeated in C and C++, so a translation unit that also includes `JSRuntimeFactoryCAPI.h` still compiles. Code that needs the rest of the C API, such as `js_runtime_factory_destroy`, imports `JSRuntimeFactoryCAPI.h` directly, as `RCTRootViewFactory.mm` already does.

With this, no header in React's umbrella reaches a stable API guard when compiled as Objective-C.

Changelog:
[Internal]

___

landed-with-radar-review

Differential Revision: D125448714

fbshipit-source-id: b7243793a6052c4b6ead001e313b96d761d012d2

Author: coado

packages/react-native/React/Runtime/RCTHermesInstanceFactory.h

@@ -5,10 +5,10 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-#import <react/runtime/JSRuntimeFactoryCAPI.h>
-
 #pragma once
 
+typedef void *JSRuntimeFactoryRef;
+
 #ifdef __cplusplus
 extern "C" {
 #endif