feat(focus): Add functionality to imperatively focus webview (#567)

*  - add focus functionality for devices without touch screen
 (faced problem while developing for android TV, cause there only remote controller for device)

* Reimplement as a ref method.

*  - remove redundant requestFocus

android/src/main/java/com/reactnativecommunity/webview/RNCWebViewManager.java

   public static final int COMMAND_POST_MESSAGE = 5;
   public static final int COMMAND_INJECT_JAVASCRIPT = 6;
   public static final int COMMAND_LOAD_URL = 7;
+  public static final int COMMAND_FOCUS = 8;
   protected static final String REACT_CLASS = "RNCWebView";
   protected static final String HTML_ENCODING = "UTF-8";
   protected static final String HTML_MIME_TYPE = "text/html";
   @Override
   public @Nullable
   Map<String, Integer> getCommandsMap() {
-    return MapBuilder.of(
+    Map map = MapBuilder.of(
       "goBack", COMMAND_GO_BACK,
       "goForward", COMMAND_GO_FORWARD,
       "reload", COMMAND_RELOAD,
       "injectJavaScript", COMMAND_INJECT_JAVASCRIPT,
       "loadUrl", COMMAND_LOAD_URL
     );
+    map.put("requestFocus", COMMAND_FOCUS);
+    return map;
   }
 
   @Override
         }
         root.loadUrl(args.getString(0));
         break;
+      case COMMAND_FOCUS:
+        root.requestFocus();
+        break;
     }
   }
 

index.d.ts

      * Executes the JavaScript string.
      */
     injectJavaScript: (script: string) => void;
+
+    /**
+     * Focuses on WebView redered page.
+     */
+    requestFocus: () => void;
 }
 
 export {WebView};

src/WebView.android.tsx

     );
   };
 
+  requestFocus = () => {
+    UIManager.dispatchViewManagerCommand(
+        this.getWebViewHandle(),
+        this.getCommands().requestFocus,
+        null,
+    );
+  };
+
   postMessage = (data: string) => {
     UIManager.dispatchViewManagerCommand(
       this.getWebViewHandle(),

src/WebView.ios.tsx

     );
   };
 
+  /**
+   * Request focus on WebView rendered page.
+   */
+  requestFocus = () => {
+    UIManager.dispatchViewManagerCommand(
+        this.getWebViewHandle(),
+        this.getCommands().requestFocus,
+        null,
+    );
+  };
+
   /**
    * Posts a message to the web view, which will emit a `message` event.
    * Accepts one argument, `data`, which must be a string.

src/WebViewTypes.ts

   postMessage: Function;
   injectJavaScript: Function;
   loadUrl: Function;
+  requestFocus: Function;
 }
 
 export interface CustomUIManager extends UIManagerStatic {