Add HMRLoadingView module for web target (#23389)

Summary:
* Added a default value for HMRLoadingView this will prevent errors from being thrown when `HMRClient` attempts to include it in a `web` context.

* [Web] [Added] - HMRLoadingView
Pull Request resolved: https://github.com/facebook/react-native/pull/23389

Differential Revision: D14045475

Pulled By: cpojer

fbshipit-source-id: df5c3cf3536af3b37eaf82342b6346bc25054319

.flowconfig

@@ -26,6 +26,9 @@
 ; require from fbjs/lib instead: require('fbjs/lib/warning')
 .*/node_modules/warning/.*
 
+; Flow doesn't support platforms
+.*/Libraries/Utilities/HMRLoadingView.js
+
 [untyped]
 .*/node_modules/@react-native-community/cli/.*/.*
 

.flowconfig.android

@@ -26,6 +26,9 @@
 ; require from fbjs/lib instead: require('fbjs/lib/warning')
 .*/node_modules/warning/.*
 
+; Flow doesn't support platforms
+.*/Libraries/Utilities/HMRLoadingView.js
+
 [untyped]
 .*/node_modules/@react-native-community/cli/.*/.*
 

Libraries/Utilities/HMRLoadingView.js

@@ -0,0 +1,23 @@
+/**
+ * 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.
+ *
+ * @format
+ * @flow strict-local
+ */
+
+'use strict';
+
+class HMRLoadingView {
+  static showMessage(message: string) {
+    // noop
+  }
+
+  static hide() {
+    // noop
+  }
+}
+
+module.exports = HMRLoadingView;