Implement changes to enable native modules auto linking (#24506)

Summary:
Replaces #24099 (original PR became detached for some reason)

Implements the template changes required to enable native modules auto-linking for both Android & iOS.

Requires the following to be merged first and an updated CLI to be published:

- [x] https://github.com/react-native-community/react-native-cli/pull/254
- [x] https://github.com/react-native-community/react-native-cli/pull/256
- [x] https://github.com/react-native-community/react-native-cli/pull/258

cc grabbou thymikee orta for review

- [ ] https://github.com/facebook/react-native/pull/24517 update CLI version)

[TEMPLATE] [FEATURE] - Enable auto-initialization/linking of react native modules for new projects
Pull Request resolved: https://github.com/facebook/react-native/pull/24506

Differential Revision: D15062701

Pulled By: cpojer

fbshipit-source-id: 65296cbec2925405fe8033de71910325e0c719bc

template/android/app/build.gradle

@@ -190,3 +190,5 @@ task copyDownloadableDepsToLibs(type: Copy) {
     from configurations.compile
     into 'libs'
 }
+
+apply from: file("../../node_modules/@react-native-community/cli-platform-android/native_modules.gradle"); applyNativeModulesAppBuildGradle(project)

template/android/app/src/main/java/com/helloworld/MainApplication.java

@@ -2,13 +2,12 @@ package com.helloworld;
 
 import android.app.Application;
 
+import com.facebook.react.PackageList;
 import com.facebook.react.ReactApplication;
 import com.facebook.react.ReactNativeHost;
 import com.facebook.react.ReactPackage;
-import com.facebook.react.shell.MainReactPackage;
 import com.facebook.soloader.SoLoader;
 
-import java.util.Arrays;
 import java.util.List;
 
 public class MainApplication extends Application implements ReactApplication {
@@ -21,9 +20,11 @@ public class MainApplication extends Application implements ReactApplication {
 
     @Override
     protected List<ReactPackage> getPackages() {
-      return Arrays.<ReactPackage>asList(
-          new MainReactPackage()
-      );
+      @SuppressWarnings("UnnecessaryLocalVariable")
+      List<ReactPackage> packages = new PackageList(this).getPackages();
+      // Packages that cannot be autolinked yet can be added manually here, for example:
+      // packages.add(new MyReactNativePackage());
+      return packages;
     }
 
     @Override

template/android/settings.gradle

@@ -1,3 +1,3 @@
 rootProject.name = 'HelloWorld'
-
+apply from: file("../node_modules/@react-native-community/cli-platform-android/native_modules.gradle"); applyNativeModulesSettingsGradle(settings)
 include ':app'

template/ios/Podfile

@@ -1,4 +1,5 @@
 platform :ios, '9.0'
+require_relative '../node_modules/@react-native-community/cli-platform-ios/native_modules'
 
 target 'HelloWorld' do
   # Pods for HelloWorld
@@ -31,6 +32,8 @@ target 'HelloWorld' do
     inherit! :search_paths
     # Pods for testing
   end
+
+  use_native_modules!
 end
 
 target 'HelloWorld-tvOS' do