FEATURE: add drafts dropdown menu (#30277)

This change adds a new dropdown trigger next to the "New Topic" button.
When clicked a menu will display a list of topic/post drafts that can be
clicked to resume the draft within the composer.

The "New Topic" button will no longer change text to show "Open Draft"
when a draft topic exists, it will still attempt to load the existing
draft if one exists (this will change later when we support multiple
drafts in a separate PR).

The "My Posts" link in desktop sidebar will now be "My Drafts" and only
appear when the current user has existing drafts.

spec/system/page_objects/components/drafts_menu.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+module PageObjects
+  module Components
+    class DraftsMenu < PageObjects::Components::Base
+      MENU_SELECTOR = ".topic-drafts-menu"
+
+      def visible?
+        has_css?(MENU_SELECTOR + "-trigger")
+      end
+
+      def hidden?
+        has_no_css?(MENU_SELECTOR + "-trigger")
+      end
+
+      def open?
+        has_css?(MENU_SELECTOR + "-content")
+      end
+
+      def closed?
+        has_no_css?(MENU_SELECTOR + "-content")
+      end
+
+      def open
+        find(MENU_SELECTOR + "-trigger").click
+      end
+
+      def draft_item_count
+        all(MENU_SELECTOR + "-content .topic-drafts-item").size
+      end
+
+      def other_drafts_count
+        find(MENU_SELECTOR + "-content .view-all-drafts span:first-child")["data-other-drafts"].to_i
+      end
+    end
+  end
+end