[RN] Fix documentation comments

* Javadoc introduced @code as a replacement of <code> and <tt> which is
  better aligned with other javadoc tags such as @link. Use it in the
  Java source code. If we switch to Kotlin, then we'll definitely use
  Markdown.

* There are more uses of @code in the JavaScript source code than <tt>
  so use @code for the sake of consistency. Eventually, I'd rather we
  switch to Markdown because it's easier on my eyes.

* Xcode is plain confused by @code and @link. The Internet says that
  Xcode supports the backquote character to denote the beginning and end
  of a string of characters which should be formatted for display as
  code but it doesn't work for me. <tt> is not rendered at all. So use
  the backquote which is rendered itself. Hopefully, if we switch to
  Markdown, then it'll be common between JavaScript and Objective-C
  source code.

android/app/src/main/java/org/jitsi/meet/MainActivity.java

@@ -38,9 +38,7 @@ import java.util.Map;
  * {@code react-native run-android}.
  */
 public class MainActivity extends JitsiMeetActivity {
-    /**
-     * {@inheritDoc}
-     */
+    @Override
     protected JitsiMeetView initializeView() {
         JitsiMeetView view = super.initializeView();
 
@@ -59,49 +57,31 @@ public class MainActivity extends JitsiMeetActivity {
                             + data);
                 }
 
-                /**
-                 * {@inheritDoc}
-                 */
                 @Override
                 public void onConferenceFailed(Map<String, Object> data) {
                     on("CONFERENCE_FAILED", data);
                 }
 
-                /**
-                 * {@inheritDoc}
-                 */
                 @Override
                 public void onConferenceJoined(Map<String, Object> data) {
                     on("CONFERENCE_JOINED", data);
                 }
 
-                /**
-                 * {@inheritDoc}
-                 */
                 @Override
                 public void onConferenceLeft(Map<String, Object> data) {
                     on("CONFERENCE_LEFT", data);
                 }
 
-                /**
-                 * {@inheritDoc}
-                 */
                 @Override
                 public void onConferenceWillJoin(Map<String, Object> data) {
                     on("CONFERENCE_WILL_JOIN", data);
                 }
 
-                /**
-                 * {@inheritDoc}
-                 */
                 @Override
                 public void onConferenceWillLeave(Map<String, Object> data) {
                     on("CONFERENCE_WILL_LEAVE", data);
                 }
 
-                /**
-                 * {@inheritDoc}
-                 */
                 @Override
                 public void onLoadConfigError(Map<String, Object> data) {
                     on("LOAD_CONFIG_ERROR", data);
@@ -112,9 +92,6 @@ public class MainActivity extends JitsiMeetActivity {
         return view;
     }
 
-    /**
-     * {@inheritDoc}
-     */
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         // As this is the Jitsi Meet app (i.e. not the Jitsi Meet SDK), we do