Annotate free functions (#37458)

Summary:
Pull Request resolved: #37458

Changelog:
Add nullability annotations for RCTInstanceRuntimeDiagnosticFlags and RCTInstanceSetRuntimeDiagnosticFlags

Reviewed By: ebgraham

Differential Revision: D45908542

fbshipit-source-id: 1f3edb566133c8e6198f39f049acf7b0284e7e5e

packages/react-native/ReactCommon/react/bridgeless/platform/ios/Core/RCTInstance.h

@@ -14,15 +14,15 @@
 #import <react/renderer/mapbuffer/MapBuffer.h>
 #import <react/utils/ContextContainer.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  * A utility to enable diagnostics mode at runtime. Useful for test runs.
  * The flags are comma-separated string tokens, or an empty string when
  * nothing is enabled.
  */
 RCT_EXTERN NSString *RCTInstanceRuntimeDiagnosticFlags(void);
-RCT_EXTERN void RCTInstanceSetRuntimeDiagnosticFlags(NSString *flags);
-
-NS_ASSUME_NONNULL_BEGIN
+RCT_EXTERN void RCTInstanceSetRuntimeDiagnosticFlags(NSString *_Nullable flags);
 
 @class RCTBundleManager;
 @class RCTInstance;