Further refinements to the Conversations panel timestamps.

See
#2707 (comment)
for the discussion.

* If the conversation last received a message today, just the time of
  the message is used, e.g. 12:03.

* If the conversation last received a message in the last week, the day
  and time of the message are used, e.g. Mon 12:03.

* If the conversation last received a message this calendar year, the
  month, day of month and time of the message are used, e.g. Mar 13 12:03.

* If the conversation last received a message in a previous calendar
  year, the date of the message is used, e.g. 13/03/2023.

Author: ianmacd

ts/components/conversation/Timestamp.tsx

@@ -58,10 +58,13 @@ export const Timestamp = (props: Props) => {
       // Today: Use the time only.
       dateString = momentValue.format('LT');
     } else if (now.diff(momentValue, 'days') < 6) {
-      // Less than a week old: Use the day only.
-      dateString = momentValue.format('ddd');
+      // Less than a week old: Use the day and time.
+      dateString = momentValue.format('ddd LT');
+    } else if (momentValue.isSame(now, 'year')) {
+      // This year: Use the month, day of month and time.
+      dateString = momentValue.format('MMM D LT');
     } else {
-      // More than a week old: Use the full date.
+      // Last year or older: Use the full date.
       dateString = momentValue.format('L');
     }
   } else {