[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.

react/features/authentication/components/styles.js

@@ -1,7 +1,7 @@
 import { BoxModel, createStyleSheet } from '../../base/styles';
 
 /**
- * The style common to <tt>LoginDialog</tt> and <tt>WaitForOwnerDialog</tt>.
+ * The style common to {@code LoginDialog} and {@code WaitForOwnerDialog}.
  */
 const dialog = {
     marginBottom: BoxModel.margin,
@@ -9,8 +9,8 @@ const dialog = {
 };
 
 /**
- * The style common to <tt>Text</tt> rendered by <tt>LoginDialog</tt> and
- * <tt>WaitForOwnerDialog</tt>.
+ * The style common to {@code Text} rendered by {@code LoginDialog} and
+ * {@code WaitForOwnerDialog}.
  */
 const text = {
 };
@@ -20,7 +20,7 @@ const text = {
  */
 export default createStyleSheet({
     /**
-     * The style of bold <tt>Text</tt> rendered by the <tt>Dialog</tt>s of the
+     * The style of bold {@code Text} rendered by the {@code Dialog}s of the
      * feature authentication.
      */
     boldDialogText: {
@@ -29,7 +29,7 @@ export default createStyleSheet({
     },
 
     /**
-     * The style of <tt>Text</tt> rendered by the <tt>Dialog</tt>s of the
+     * The style of {@code Text} rendered by the {@code Dialog}s of the
      * feature authentication.
      */
     dialogText: {
@@ -37,7 +37,7 @@ export default createStyleSheet({
     },
 
     /**
-     * The style of <tt>TextInput</tt> rendered by the <tt>Dialog</tt>s of the
+     * The style of {@code TextInput} rendered by the {@code Dialog}s of the
      * feature authentication.
      */
     dialogTextInput: {
@@ -48,7 +48,7 @@ export default createStyleSheet({
     },
 
     /**
-     * The style of <tt>LoginDialog</tt>.
+     * The style of {@code LoginDialog}.
      */
     loginDialog: {
         ...dialog,
@@ -57,7 +57,7 @@ export default createStyleSheet({
     },
 
     /**
-     * The style of <tt>WaitForOwnerDialog</tt>.
+     * The style of {@code WaitForOwnerDialog}.
      */
     waitForOwnerDialog: {
         ...dialog,