UX: chat drawer increase unread channel visibility (#28731)

This change increases the visibility of unread channels to make them stand out more in drawer mode (desktop).

When a channel is unread:

- it floats to the top;
- when multiple channels are unread, they are sorted alphabetically (equal to how it’s done on mobile)
- the unread indicator blue dot moves to directly right of the channel name

plugins/chat/spec/system/channel_settings_page_spec.rb

@@ -100,7 +100,7 @@ RSpec.describe "Channel - Info - Settings page", type: :system do
       expect(page.find(".c-channel-settings__name")["innerHTML"].strip).to eq(
         "<script>alert('hello')</script>",
       )
-      expect(page.find(".chat-channel-name__label")["innerHTML"].strip).to eq(
+      expect(page.find(".chat-channel-name__label")["innerHTML"].strip).to include(
         "<script>alert('hello')</script>",
       )
     end