boxes: Use user_ids in autocomplete for ambiguous user mentions.

Prior to this commit, user mentions through autocomplete used only
names in the typeahead. This commit appends `user_id`s to all the
multiple instances of the same name to use the **Name|User_id** format of
user mentions. The appended user_id would serve as a distinction
between users having the same name.

Tests updated.

Author: prah23

zulipterminal/ui_tools/boxes.py

@@ -445,11 +445,23 @@ def autocomplete_users(self, text: str, prefix_string: str
                                        reverse=True)
 
         user_names = [user['full_name'] for user in sorted_matching_users]
+
+        user_name_duplicates = [user_name
+                                for count, user_name in enumerate(user_names)
+                                if user_name in user_names[:count]]
+
+        user_names_with_distinct_duplicates = [
+            f"{user['full_name']}|{user['user_id']}"
+            if user['full_name'] in user_name_duplicates
+            else user['full_name']
+            for user in sorted_matching_users
+        ]
+
         extra_prefix = "{}{}".format(
             '*' if prefix_string[-1] != '*' else '',
             '*' if prefix_string[-2:] != '**' else '',
         )
-        user_typeahead = format_string(user_names,
+        user_typeahead = format_string(user_names_with_distinct_duplicates,
                                        prefix_string + extra_prefix + '{}**')
 
         return user_typeahead, user_names