Transform mixed to unknown in xplat/js (#55048)

Summary:
Pull Request resolved: #55048

Transform leftovers dropped by conflicts

Command:
```
js1 flow-runner codemod flow/transformUtilityType --legacy-type='mixed' --format-files=false xplat/js
```

drop-conflicts

Reviewed By: SamChou19815

Differential Revision: D90131601

fbshipit-source-id: 6497ce36dfed3b3ebe2706cf90909447b36e397a

Author: marcoww6

packages/react-native/Libraries/BatchedBridge/NativeModules.js

@@ -50,7 +50,7 @@ function genModule(
     return {name: moduleName};
   }
 
-  const module: {[string]: mixed} = {};
+  const module: {[string]: unknown} = {};
   methods &&
     methods.forEach((methodName, methodID) => {
       const isPromise =
@@ -99,7 +99,7 @@ function loadModule(name: string, moduleID: number): ?{...} {
 function genMethod(moduleID: number, methodID: number, type: MethodType) {
   let fn = null;
   if (type === 'promise') {
-    fn = function promiseMethodWrapper(...args: Array<mixed>) {
+    fn = function promiseMethodWrapper(...args: Array<unknown>) {
       // In case we reject, capture a useful stack trace here.
       /* $FlowFixMe[class-object-subtyping] added when improving typing for
        * this parameters */
@@ -122,7 +122,7 @@ function genMethod(moduleID: number, methodID: number, type: MethodType) {
       });
     };
   } else {
-    fn = function nonPromiseMethodWrapper(...args: Array<mixed>) {
+    fn = function nonPromiseMethodWrapper(...args: Array<unknown>) {
       const lastArg = args.length > 0 ? args[args.length - 1] : null;
       const secondLastArg = args.length > 1 ? args[args.length - 2] : null;
       const hasSuccessCallback = typeof lastArg === 'function';
@@ -133,9 +133,11 @@ function genMethod(moduleID: number, methodID: number, type: MethodType) {
           'Cannot have a non-function arg after a function arg.',
         );
       // $FlowFixMe[incompatible-type]
-      const onSuccess: ?(mixed) => void = hasSuccessCallback ? lastArg : null;
-      // $FlowFixMe[incompatible-type]
-      const onFail: ?(mixed) => void = hasErrorCallback ? secondLastArg : null;
+      const onSuccess: ?(unknown) => void = hasSuccessCallback ? lastArg : null;
+      const onFail: ?(unknown) => void = hasErrorCallback
+        ? // $FlowFixMe[incompatible-type]
+          secondLastArg
+        : null;
       // $FlowFixMe[unsafe-addition]
       const callbackCount = hasSuccessCallback + hasErrorCallback;
       const newArgs = args.slice(0, args.length - callbackCount);