iOS: Update RCTAlertManager to use new RCTAlertController (#29295)

Summary:
This should fix #29082 and #10471

Currently when an alert is being shown while a modal is being dismissed, it causes the alert not to show and In some cases it causes the UI to become unresponsive. I think this was caused by using RCTPresentedViewController to try and display the Alert the currently presented view. The View the Alert was going to be shown on is dismissed and the modal doesn't show. I implemented a new RCTAlertController to show the alert on top of the view, the modal being dismissed should now not interfere with the alert being shown.

## Changelog

[iOS] [Fixed] - Fixed showing Alert while closing a Modal

Pull Request resolved: #29295

Test Plan:
To recreate the bug:

1. npx react-native init Test --version 0.63.0-rc.1
2. Paste the following code into App.js

```javascript
/**
 * Sample React Native App
 * https://github.com/facebook/react-native
 *
 * format
 * flow strict-local
 */

import React from 'react';
import {
  SafeAreaView,
  StyleSheet,
  View,
  Text,
  StatusBar,
  Modal,
  Alert
} from 'react-native';

const App: () => React$Node = () => {
  const [visible, setVisible] = React.useState(false)

  const onShowModal = () => {
    setVisible(true)
  }

  onCloseBroken = () => {
    setVisible(false)
    Alert.alert('Alert', 'Alert won\'t show')
  }

  onCloseWorking = () => {
    setVisible(false)
    setTimeout(() => Alert.alert('Alert', 'Works fine'), 10)
  }

  return (
    <>
      <StatusBar barStyle="dark-content" />
      <SafeAreaView style={styles.container}>
        <Text onPress={onShowModal}>Show modal</Text>
      </SafeAreaView>
      <Modal animationType="fade" visible={visible} onRequestClose={onCloseWorking} >
        <View style={styles.container}>
          <Text onPress={onCloseBroken}>Close modal immediately</Text>
          <Text onPress={onCloseWorking}>Close modal with delay</Text>
        </View>
      </Modal>
    </>
  )
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    alignItems: 'center',
    justifyContent: 'space-around',
  },
})

export default App

```

3. cd Test && npx react-native run-ios
4. Show the modal and click the `Close modal immediately` button

The first button doesn't show the alert, the second does because it gets rendered after the modal view is dismissed. After this commit, the alert always shows on top of every view properly. You can test by pointing the react native package to my branch by modifying the package json file like this

```
    "react-native": "https://github.com/devon94/react-native.git#fix-ios-modal"
```

I was unable to reproduce the case where it causes the UI to be responsive in the test app but was able to reproduce it in our react native app at work. I can provide a video later if needed but the code is too complex to simplify into a test case.

Reviewed By: sammy-SC

Differential Revision: D22783371

Pulled By: PeteTheHeat

fbshipit-source-id: 3e359645c610074ea855ee5686c59bdb9d6b696b

RNTester/Podfile.lock

@@ -505,7 +505,7 @@ SPEC CHECKSUMS:
   RCTTypeSafety: 1ade47a69b092cddf1e4ea21e0c5bdc65cc950b4
   React: cafb3c2321f7df55ce90dbf29d513799a79e4418
   React-callinvoker: 0dada022d38b73e6e15b33e2a96476153f79bbf6
-  React-Core: 22edbf19e3f430ce23111ead6741579f7a591ff2
+  React-Core: 6c6f6c40bb1e031de8a0fafce08c010edfef09ab
   React-CoreModules: d13d148c851af5780f864be74bc2165140923dc7
   React-cxxreact: 4661b3295e62c6eaada084e2f826c70c71ef11ea
   React-jsi: fe94132da767bfc4801968c2a12abae43e9a833e

React/CoreModules/RCTAlertController.h

@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import <UIKit/UIKit.h>
+
+@interface RCTAlertController : UIAlertController
+
+- (void)show:(BOOL)animated completion:(void (^)(void))completion;
+
+@end

React/CoreModules/RCTAlertController.m

@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import <React/RCTUtils.h>
+
+#import "RCTAlertController.h"
+
+@interface RCTAlertController ()
+
+@property (nonatomic, strong) UIWindow *alertWindow;
+
+@end
+
+@implementation RCTAlertController
+
+- (UIWindow *)alertWindow
+{
+  if (_alertWindow == nil) {
+    _alertWindow = [[UIWindow alloc] initWithFrame:RCTSharedApplication().keyWindow.bounds];
+    _alertWindow.rootViewController = [UIViewController new];
+    _alertWindow.windowLevel = UIWindowLevelAlert + 1;
+  }
+  return _alertWindow;
+}
+
+- (void)show:(BOOL)animated completion:(void (^)(void))completion
+{
+  [self.alertWindow makeKeyAndVisible];
+  [self.alertWindow.rootViewController presentViewController:self animated:animated completion:completion];
+}
+
+@end

React/CoreModules/RCTAlertManager.mm

@@ -15,6 +15,7 @@
 #import <React/RCTUtils.h>
 
 #import "CoreModulesPlugins.h"
+#import "RCTAlertController.h"
 
 @implementation RCTConvert (UIAlertViewStyle)
 
@@ -99,29 +100,9 @@ - (void)invalidate
     }
   }
 
-  UIViewController *presentingController = RCTPresentedViewController();
-  if (presentingController == nil) {
-    RCTLogError(@"Tried to display alert view but there is no application window. args: %@", @{
-      @"title" : args.title() ?: [NSNull null],
-      @"message" : args.message() ?: [NSNull null],
-      @"buttons" : RCTConvertOptionalVecToArray(
-          args.buttons(),
-          ^id(id<NSObject> element) {
-            return element;
-          })
-          ?: [NSNull null],
-      @"type" : args.type() ?: [NSNull null],
-      @"defaultValue" : args.defaultValue() ?: [NSNull null],
-      @"cancelButtonKey" : args.cancelButtonKey() ?: [NSNull null],
-      @"destructiveButtonKey" : args.destructiveButtonKey() ?: [NSNull null],
-      @"keyboardType" : args.keyboardType() ?: [NSNull null],
-    });
-    return;
-  }
-
-  UIAlertController *alertController = [UIAlertController alertControllerWithTitle:title
-                                                                           message:nil
-                                                                    preferredStyle:UIAlertControllerStyleAlert];
+  RCTAlertController *alertController = [RCTAlertController alertControllerWithTitle:title
+                                                                             message:nil
+                                                                      preferredStyle:UIAlertControllerStyleAlert];
   switch (type) {
     case RCTAlertViewStylePlainTextInput: {
       [alertController addTextFieldWithConfigurationHandler:^(UITextField *textField) {
@@ -170,7 +151,7 @@ - (void)invalidate
     } else if ([buttonKey isEqualToString:destructiveButtonKey]) {
       buttonStyle = UIAlertActionStyleDestructive;
     }
-    __weak UIAlertController *weakAlertController = alertController;
+    __weak RCTAlertController *weakAlertController = alertController;
     [alertController
         addAction:[UIAlertAction
                       actionWithTitle:buttonTitle
@@ -202,7 +183,7 @@ - (void)invalidate
   [_alertControllers addObject:alertController];
 
   dispatch_async(dispatch_get_main_queue(), ^{
-    [presentingController presentViewController:alertController animated:YES completion:nil];
+    [alertController show:YES completion:nil];
   });
 }