compose: Allow message_id to be passed to respond_to_message.

Up until now, the currently selected message was the one that was always
responded to. Now if there's a message_id passed in, we'll use that
message instead, otherwise we'll fall back to the selected message.

This is a prep commit for allowing quoting and replying while editing
a message sent earlier.

web/src/compose_reply.js

@@ -42,7 +42,8 @@ export function respond_to_message(opts) {
         }
         message = message_opts.message;
     } else {
-        message = message_lists.current.selected_message();
+        message =
+            message_lists.current.get(opts.message_id) || message_lists.current.selected_message();
 
         if (message === undefined) {
             // empty narrow implementation

web/tests/compose_actions.test.js

@@ -263,10 +263,11 @@ test("respond_to_message", ({override, override_rewire, mock_template}) => {
         type: "private",
         sender_id: person.user_id,
     };
-    override(message_lists.current, "selected_message", () => msg);
+    override(message_lists.current, "get", (id) => (id === 100 ? msg : undefined));
 
     let opts = {
         reply_type: "personal",
+        message_id: 100,
     };
 
     respond_to_message(opts);
@@ -286,6 +287,7 @@ test("respond_to_message", ({override, override_rewire, mock_template}) => {
         stream_id: denmark.stream_id,
         topic: "python",
     };
+    override(message_lists.current, "selected_message", () => msg);
 
     opts = {};
 
@@ -319,6 +321,7 @@ test("reply_with_mention", ({override, override_rewire, mock_template}) => {
         sender_full_name: "Bob Roberts",
         sender_id: 40,
     };
+    override(message_lists.current, "get", (_id) => undefined);
     override(message_lists.current, "selected_message", () => msg);
 
     let syntax_to_insert;
@@ -369,6 +372,7 @@ test("quote_and_reply", ({disallow, override, override_rewire}) => {
     override_private_message_recipient({override});
 
     let selected_message;
+    override(message_lists.current, "get", (_id) => undefined);
     override(message_lists.current, "selected_message", () => selected_message);
 
     let expected_replacement;