refactor: optimize plugins for angular treeshaking

BREAKING CHANGE: You can remove the plugin import from the app.module.ts because of the changed Inject decorator

src/@ionic-native/plugins/keyboard/index.ts

@@ -30,7 +30,9 @@ import { Observable } from 'rxjs';
   repo: 'https://github.com/ionic-team/cordova-plugin-ionic-keyboard',
   platforms: ['Android', 'iOS']
 })
-@Injectable()
+@Injectable({
+  providedIn: 'root'
+})
 export class Keyboard extends IonicNativePlugin {
   /**
    * Check keyboard status visible or not.