edit_history: Respect time format setting (12h/24h).

Previously, the edit history modal did not respect the time format
setting (whether to show times in 12-hour or 24-hour format) when
displaying message edit times (#15171).

This commit fixes that by passing the edit times to
timerender.stringify_time(), which takes that setting into account,
instead of just doing a static string formatting operation.

This bug has existed since February 2017, when the edit history UI
was first added in 1a697b6e02.

Fixes #15171.

static/js/message_edit_history.js

@@ -13,7 +13,7 @@ exports.fetch_and_render_message_history = function (message) {
                 const time = new XDate(msg.timestamp * 1000);
                 const datestamp = time.toDateString();
                 const item = {
-                    timestamp: time.toString('h:mm TT'),
+                    timestamp: timerender.stringify_time(time),
                     display_date: time.toString("MMMM d, yyyy"),
                     show_date_row: datestamp !== prev_datestamp,
                 };