FEATURE: Thread indicator improvements and participants (#21909)

This commit adds the initial part of thread indicator improvements:

* Show the reply count, last reply date and excerpt,
and the participants of the thread's avatars and
count of additional participants
* Add a participants component for the thread that
can be reused for the list
* Add a query class to get the thread participants
* Live update the thread indicator more consistently
with the last reply and participant details
image image

In subsequent PRs we will cache the participants since
they do not change often, and improve the thread list
further with participants.

This commit also adds a showPresence boolean (default
true) to ChatUserAvatar, since we don't want to show the
online indicator for thread participants.

---------

Co-authored-by: chapoi <charlie@discourse.org>

plugins/chat/spec/components/chat/message_creator_spec.rb

@@ -769,11 +769,6 @@ describe Chat::MessageCreator do
 
         it "does not create a thread membership if one exists" do
           Fabricate(:user_chat_thread_membership, user: user1, thread: existing_thread)
-          Fabricate(
-            :user_chat_thread_membership,
-            user: existing_thread.original_message_user,
-            thread: existing_thread,
-          )
           expect {
             described_class.create(
               chat_channel: public_chat_channel,

plugins/chat/spec/components/chat/message_updater_spec.rb

@@ -610,6 +610,29 @@ describe Chat::MessageUpdater do
     end
   end
 
+  context "when the message is in a thread" do
+    fab!(:message) do
+      Fabricate(
+        :chat_message,
+        user: user1,
+        chat_channel: public_chat_channel,
+        thread: Fabricate(:chat_thread, channel: public_chat_channel),
+      )
+    end
+
+    it "publishes a MessageBus event to update the original message metadata" do
+      messages =
+        MessageBus.track_publish("/chat/#{public_chat_channel.id}") do
+          Chat::MessageUpdater.update(
+            guardian: guardian,
+            chat_message: message,
+            new_content: "some new updated content",
+          )
+        end
+      expect(messages.find { |m| m.data["type"] == "update_thread_original_message" }).to be_present
+    end
+  end
+
   describe "watched words" do
     fab!(:watched_word) { Fabricate(:watched_word) }