recent_topics: Save offset when navigating from narrow or "all".

This is partially a prep commit to correctly saving/restoring the
position of the blue message select box when using browser
back/forward navigation, and partially a bug fix that ensures that
switching from "all_messages" to "recent_topics" preserves one's
position in "all_messages".
Note that this is with regards to saving the visual position of the
selected message, not about saving "which message was selected".

frontend_tests/node_tests/recent_topics.js

@@ -97,9 +97,10 @@ mock_esm("../../static/js/muted_topics", {
         return false;
     },
 });
-mock_esm("../../static/js/narrow", {
+const narrow = mock_esm("../../static/js/narrow", {
     set_narrow_title: noop,
     hide_mark_as_read_turned_off_banner: noop,
+    has_shown_message_list_view: true,
 });
 mock_esm("../../static/js/recent_senders", {
     get_topic_recent_senders: () => [1, 2],
@@ -338,7 +339,9 @@ function test(label, f) {
     });
 }
 
-test("test_recent_topics_show", ({mock_template}) => {
+test("test_recent_topics_show", ({mock_template, override}) => {
+    override(narrow, "save_pre_narrow_offset_for_reload", () => {});
+
     // Note: unread count and urls are fake,
     // since they are generated in external libraries
     // and are not to be tested here.

static/js/narrow.js

@@ -114,6 +114,7 @@ export function save_pre_narrow_offset_for_reload() {
 }
 
 export let narrow_title = "home";
+export let has_shown_message_list_view = false;
 
 export function set_narrow_title(title) {
     narrow_title = title;
@@ -292,6 +293,7 @@ export function activate(raw_operators, opts) {
     // populating the new narrow, so we update our narrow_state.
     // From here on down, any calls to the narrow_state API will
     // reflect the upcoming narrow.
+    has_shown_message_list_view = true;
     narrow_state.set_current_filter(filter);
 
     const excludes_muted_topics = narrow_state.excludes_muted_topics();
@@ -882,6 +884,7 @@ export function deactivate(coming_from_recent_topics = false) {
     }
 
     narrow_state.reset_current_filter();
+    has_shown_message_list_view = true;
 
     $("body").removeClass("narrowed_view");
     $("#zfilt").removeClass("focused_table");

static/js/recent_topics_ui.js

@@ -622,6 +622,10 @@ export function complete_rerender() {
 }
 
 export function show() {
+    if (narrow.has_shown_message_list_view) {
+        narrow.save_pre_narrow_offset_for_reload();
+    }
+
     if (is_visible()) {
         // If we're already visible, E.g. because the user hit Esc
         // while already in the recent topics view, do nothing.