Remove dead include from RCTInstance.h (#58181)

Summary:
Pull Request resolved: #58181

Under the C++ Stable API RFC, `jserrorhandler:jserrorhandler` is a "for frameworks" module, but it was still reached from a public header:

- The iOS and macOS `RCTInstance.h` included `react/runtime/ReactInstance.h`, which in turn includes `jserrorhandler/JsErrorHandler.h`. Neither `RCTInstance.h` names `ReactInstance` or `JsErrorHandler`; the only C++ types they use are `JSRuntimeFactory` and `jsinspector_modern::HostTarget`, both already included directly. The include is dead and is simply removed.
- `RCTInstance.mm` does name both types and was relying on the include transitively, so `react/runtime/ReactInstance.h` and `jserrorhandler/JsErrorHandler.h` move to the implementation file on both platforms.

Changelog: [Internal]

Reviewed By: javache

Differential Revision: D117842042

fbshipit-source-id: 1b1e1545acbfc01be12d2af0ddc84d6b1ecf4ca3

Author: j-piasecki

packages/react-native/ReactCommon/react/runtime/platform/ios/ReactCommon/RCTInstance.h

@@ -13,7 +13,6 @@
 #import <React/RCTJavaScriptLoader.h>
 #import <jsinspector-modern/ReactCdp.h>
 #import <react/runtime/JSRuntimeFactory.h>
-#import <react/runtime/ReactInstance.h>
 
 #import "RCTContextContainerHandling.h"
 

packages/react-native/ReactCommon/react/runtime/platform/ios/ReactCommon/RCTInstance.mm

@@ -37,10 +37,12 @@
 #import <ReactCommon/RCTTurboModuleManager.h>
 #import <ReactCommon/RuntimeExecutor.h>
 #import <cxxreact/ReactMarker.h>
+#import <jserrorhandler/JsErrorHandler.h>
 #import <jsinspector-modern/InspectorFlags.h>
 #import <jsinspector-modern/ReactCdp.h>
 #import <jsireact/JSIExecutor.h>
 #import <react/featureflags/ReactNativeFeatureFlags.h>
+#import <react/runtime/ReactInstance.h>
 #import <react/utils/ContextContainer.h>
 #import <react/utils/FollyConvert.h>
 #import <react/utils/ManagedObjectWrapper.h>