Decouple Hermes factory header from C++ paths

Summary:
`RCTHermesInstanceFactory.h` is part of React's umbrella header, but it imported a lower-level C++ header that was unavailable while a SwiftPM Release build compiled the `React` module. Forward-declare the opaque `JSRuntimeFactoryRef` handle instead of relying on transitive C++ header search paths.

This preserves the C ABI and mirrors the existing self-contained declaration used by `RCTJSRuntimeConfiguratorProtocol.h`. The first observed failure was at `024b474ce92ba66744af602ee67691cd11498485`; the immediately preceding `main` SPM Release run passed, but that commit only changed `RCTInstance.mm`, so source-level attribution remains uncertain. The risk is limited to keeping two equivalent opaque aliases in sync; both remain `void *`.

Validation covered the internal Apple runtime target, all React Native C++ API snapshot configurations, formatter, and lint. A full SwiftPM/Xcode rerun was not available on the Linux build host.

Changelog:
[iOS][Fixed] - Fix SwiftPM Release builds failing to compile the React umbrella module

Differential Revision: D123142962

Author: cortinico

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

@@ -5,12 +5,14 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-#import <react/runtime/JSRuntimeFactoryCAPI.h>
-
 #pragma once
 
+// Forward declaration keeps this umbrella header independent of C++ header search paths.
 #ifdef __cplusplus
+using JSRuntimeFactoryRef = void *;
 extern "C" {
+#else
+typedef void *JSRuntimeFactoryRef;
 #endif
 
 JSRuntimeFactoryRef jsrt_create_hermes_factory(void);