Fixed method invoke when both nullable and __unused exist (#23726)

Summary:
We have parse code to try to support exported method parameter annotated `__unused` and `nullable`, but actually, seems we don't support it entirely, for example, we parse `__unused` firstly, then we parse `nullable`, actually, this case not exist, because `nullable` macro must appear right after `(`, before `__unused`, so we can't parse success, leads to error signature and crash.

[iOS] [Fixed] - Fixed method invoke when both nullable and __unused exist
Pull Request resolved: https://github.com/facebook/react-native/pull/23726

Differential Revision: D14298563

Pulled By: cpojer

fbshipit-source-id: 934e1d384a5d67b7bbf117fd2dec51f50979c979

React/Base/RCTModuleMethod.mm

@@ -90,8 +90,8 @@ static BOOL RCTParseSelectorPart(const char **input, NSMutableString *selector)
 
 static BOOL RCTParseUnused(const char **input)
 {
-  return RCTReadString(input, "__unused") ||
-         RCTReadString(input, "__attribute__((unused))");
+  return RCTReadString(input, "__attribute__((unused))") ||
+         RCTReadString(input, "__unused");
 }
 
 static RCTNullability RCTParseNullability(const char **input)
@@ -145,16 +145,33 @@ NSString *RCTParseMethodSignature(const char *input, NSArray<RCTMethodArgument *
     if (RCTReadChar(&input, '(')) {
       RCTSkipWhitespace(&input);
       
-      BOOL unused = RCTParseUnused(&input);
+      // 5 cases that both nullable and __unused exist
+      // 1: foo:(nullable __unused id)foo 2: foo:(nullable id __unused)foo
+      // 3: foo:(__unused id _Nullable)foo 4: foo:(id __unused _Nullable)foo
+      // 5: foo:(id _Nullable __unused)foo
+      RCTNullability nullability = RCTParseNullability(&input);
       RCTSkipWhitespace(&input);
       
-      RCTNullability nullability = RCTParseNullability(&input);
+      BOOL unused = RCTParseUnused(&input);
       RCTSkipWhitespace(&input);
 
       NSString *type = RCTParseType(&input);
       RCTSkipWhitespace(&input);
+      
       if (nullability == RCTNullabilityUnspecified) {
         nullability = RCTParseNullabilityPostfix(&input);
+        RCTSkipWhitespace(&input);
+        if (!unused) {
+          unused = RCTParseUnused(&input);
+          RCTSkipWhitespace(&input);
+          if (unused && nullability == RCTNullabilityUnspecified) {
+            nullability = RCTParseNullabilityPostfix(&input);
+            RCTSkipWhitespace(&input);
+          }
+        }
+      } else if (!unused) {
+        unused = RCTParseUnused(&input);
+        RCTSkipWhitespace(&input);
       }
       [args addObject:[[RCTMethodArgument alloc] initWithType:type
                                                   nullability:nullability