Automatically reset text area on keyboard events if native OSK is enabled/assumed. Hide text area via CSS.

guacamole/src/main/webapp/client.xhtml

@@ -54,10 +54,8 @@
 
         </div>
 
-        <input id="eventTarget"
-               type="text"
-               style="width: 0; height: 0; position: fixed; opacity: 0"
-               value="x"/>
+        <!-- Keyboard event target for platforms with native OSKs -->
+        <textarea id="eventTarget">GUAC</textarea>
 
         <!-- Display -->
         <div id="display">