accessibility: Add button role and tabindex to sender names.

This facilitates interacting with them via keyboard.

Author: ndarilek

static/templates/single_message.handlebars

@@ -15,7 +15,7 @@
                             </div>
                             {{#if status_message}}
                                 <span class="sender-status">
-                                    <span class="sender_name-in-status auto-select sender_info_hover">{{msg/sender_full_name}}</span>
+                                    <span class="sender_name-in-status auto-select sender_info_hover" role="button" tabindex="0">{{msg/sender_full_name}}</span>
                                     {{#if sender_is_bot}}
                                     <i class="zulip-icon bot" aria-label="{{t 'Bot' }}"></i>
                                     {{/if}}
@@ -27,7 +27,7 @@
                                     {{/if_and}}
                                 </span>
                             {{else}}
-                                <span class="sender_name auto-select">{{msg/sender_full_name}}</span>
+                                <span class="sender_name auto-select" role="button" tabindex="0">{{msg/sender_full_name}}</span>
                                 {{#if sender_is_bot}}
                                 <i class="zulip-icon bot" aria-label="{{t 'Bot' }}"></i>
                                 {{/if}}