UI: redesigned settings/members (#23804)

This PR is a first step towards private groups. It redesigns settings/members area of a channel and also drops the "about" page which is now mixed into settings.

This commit is also:
- introducing chat-form, a small DSL to create forms, ideally I would want something in core for this
- introducing a DToggleSwitch page object component to simplify testing toggles
- migrating various components to gjs

plugins/chat/spec/system/drawer_spec.rb

@@ -24,7 +24,7 @@ RSpec.describe "Drawer", type: :system do
         drawer_page.open_channel(channel)
         page.find(".chat-channel-title").click
 
-        expect(page).to have_current_path("/chat/c/#{channel.slug}/#{channel.id}/info/about")
+        expect(page).to have_current_path("/chat/c/#{channel.slug}/#{channel.id}/info/settings")
       end
     end
   end