Drop RCT_EXPORT_METHOD from RCTAppState TurboModule (#57676)

Summary:

Changelog: [Internal]

`RCTAppState` is a TurboModule: it conforms to `NativeAppStateSpec` and implements `getTurboModule:` returning the codegen'd `...SpecJSI`. For TurboModules, the JS->ObjC dispatch is driven by codegen (the generated spec supplies the `selector` and argument kinds, invoked at runtime via `NSMethodSignature` / `NSInvocation`), not by the `RCT_EXPORT_METHOD` macro's `__rct_export__` metadata.

The exported methods here are async-void with concrete parameter types (no generic `id` requiring `RCTConvert` coercion), so the macro is not functionally required. Convert them to plain ObjC method declarations; conformance to the codegen'd `NativeAppStateSpec` protocol keeps compiler-enforced signature parity.

Signature-only refactor with no change to the JS-facing API. Sync methods, methods with `id` params, and `constantsToExport` are intentionally left untouched.

Differential Revision: D113579877

Author: christophpurrer

packages/react-native/React/CoreModules/RCTAppState.mm

@@ -135,7 +135,7 @@ - (void)handleAppStateDidChange:(NSNotification *)notification
 /**
  * Get the current background/foreground state of the app
  */
-RCT_EXPORT_METHOD(getCurrentAppState : (RCTResponseSenderBlock)callback error : (__unused RCTResponseSenderBlock)error)
+- (void)getCurrentAppState:(RCTResponseSenderBlock)callback error:(__unused RCTResponseSenderBlock)error
 {
   callback(@[ @{@"app_state" : RCTCurrentAppState()} ]);
 }