DEV: rework the chat-live-pane

This PR is introducing glimmer usage in the chat-live-pane, for components but also for models. RestModel usage has been dropped in favor of native classes.

Other changes/additions in this PR:

- sticky dates, scrolling will now keep the date separator of the current section at the top of the screen
- better unread management, marking a channel as unread will correctly mark the correct message and not mark the whole channel as read. Tracking state will also now correctly return unread count and unread mentions.
- adds an animation on bottom arrow
- better scrolling behavior, we should now always correctly keep the scroll position while loading more
- reactions are now more reactive, and will update their tooltip without needed to close/reopen it
- skeleton has been improved with placeholder images and reactions
- when making a reaction on the desktop message actions, the menu won't move anymore
- simplify logic and stop maintaining a list of unloaded messages

plugins/chat/spec/system/create_channel_spec.rb

@@ -81,6 +81,7 @@ RSpec.describe "Create channel", type: :system, js: true do
         chat_page.visit_browse
         chat_page.new_channel_button.click
         channel_modal.select_category(private_category_1)
+        expect(page).to have_no_css(".loading-permissions")
 
         expect(channel_modal.create_channel_hint["innerHTML"].strip).to include(
           "<script>e</script>",