docs(webpack): update custom application and activity article (#1254)

* docs(webpack): add custom application and activity section

* docs(webpack): minor tweaks

* docs(webpack): update extend article

Move custom application and activity webpack configuration information to the `extend-application-activity.md` article.

* docs(webpack): minor tweaks

Author: Vasil Chimev

docs/core-concepts/android-runtime/advanced-topics/extend-application-activity.md

@@ -78,14 +78,29 @@ The following steps are needed to create custom native `android.app.Application`
 
     >This modification is required by the native platform; it basically tells Android that your custom `Application` class will be used as the main entry point of the application.
 
+4. In order to build the app with [webpack](../../../performance-optimizations/bundling-with-webpack.md), the extended Android application should be added as an [entry](https://github.com/NativeScript/nativescript-dev-webpack/blob/master/demo/AngularApp/webpack.config.js#L71) to the `webpack.config.js` file.
+
+    ```javascript
+        entry: {
+            bundle: entryPath,
+            application: "./application.android",
+        },
+    ```
+
+    In this way, the source code of [`application.android.ts`](https://github.com/NativeScript/nativescript-dev-webpack/blob/master/demo/AngularApp/app/application.android.ts) is bundled separately as `application.js` file which is loaded from the native `Application.java` class on launch.
+
+    The `bundle.js` and `vendor.js` files are not loaded early enough in the application launch. That's why the logic in `application.android.ts` is needed to be bundled separately in order to be loaded as early as needed in the application lifecycle.
+
+    > Note: This approach won't work if `aplication.android.ts` requires external modules.
+
 ## Extending Activity
 The core modules ship with a default `android.app.Activity` implementation, which ensures they alone are sufficient to bootstrap an empty NativeScript application, without forcing users to declare their custom `Activity` in every project. When needed, however, users may still specify custom `Activity` implementation and use it to bootstrap the application. The following code demonstrates how this can be done:
 
-1.  Create a new JavaScript file in your `app` folder - name it `activity.android.js`
+1. Create a new JavaScript file in your `app` folder - name it `activity.android.js`
 
     >Note the `*.android` suffix - we want this file packaged for Android only.
 
-2.  Declare the extend:
+2. Declare the extend:
 
     ```javascript
     const frame = require("ui/frame");
@@ -180,5 +195,17 @@ The core modules ship with a default `android.app.Activity` implementation, whic
             android:configChanges="keyboardHidden|orientation|screenSize">
     ```
 
+4. In order to build the app with [webpack](../../../performance-optimizations/bundling-with-webpack.md), the absolute path to the file where the Android activity is extended should be added to the [`appComponents`](https://github.com/NativeScript/nativescript-dev-webpack/blob/master/demo/AngularApp/webpack.config.js#L19) array.
+
+    ```javascript
+        const appComponents = [
+            "tns-core-modules/ui/frame",
+            "tns-core-modules/ui/frame/activity",
+            resolve(__dirname, "app/activity.android.ts"),
+        ];
+    ```
+
+    In this way and with the default config, these components [get](https://github.com/NativeScript/nativescript-dev-webpack/blob/master/demo/AngularApp/webpack.config.js#L109-L116) in the common *vendor.js* chunk and are required by the [`android-app-components-loader`](https://github.com/NativeScript/nativescript-dev-webpack/blob/master/demo/AngularApp/webpack.config.js#L146-L149).
+
 ## See Also
 * [How Extend Works](../generator/extend-class-interface.md)

docs/performance-optimizations/bundling-with-webpack.md

@@ -205,6 +205,10 @@ function logMessage(message) {
 }
 ```
 
+## Custom Application and Activity
+
+NativeScript provides a way to create custom `android.app.Application` and `android.app.Activity` implementations. Please, refer to [this](../core-concepts/android-runtime/advanced-topics/extend-application-activity) documentation article for a detail description of how to achieve these as well as how to configure and bundle such a project.
+
 ## Debugging Common Errors
 
 Webpack bundling can fail for different reasons. It sometimes fails to resolve certain modules, or it generates code that breaks at runtime. We'll try to cover a few common failure reasons with steps to resolve them in the following sections.