FEATURE: Force admin sidebar for all admins in admin_sidebar_enabled_groups and handle legacy "hamburger dropdown" in this mode (#26899)

Some sites are still on the legacy "hamburger dropdown"
navigation_menu setting. In this case to avoid confusion,
we want to show both the sidebar icon and the header dropdown
hamburger when visiting the admin portal. Otherwise, the
hamburger switches sides from right to left for admins
and takes on different behaviour.

The hamburger in this case _only_ shows the main panel, not
other sidebar panels like the admin one.

spec/system/page_objects/components/navigation_menu/header_dropdown.rb

@@ -6,10 +6,41 @@ module PageObjects
       class HeaderDropdown < Base
         def open
           find(".header-dropdown-toggle.hamburger-dropdown").click
-          expect(page).to have_css(".sidebar-hamburger-dropdown")
           self
         end
 
+        def close
+          open
+        end
+
+        def has_sidebar_panel?(panel)
+          has_css?(
+            ".sidebar-hamburger-dropdown .sidebar-section-wrapper[data-section-name=\"#{panel_id(panel)}\"]",
+          )
+        end
+
+        def has_no_sidebar_panel?(panel)
+          has_no_css?(
+            ".sidebar-hamburger-dropdown .sidebar-section-wrapper[data-section-name=\"#{panel_id(panel)}\"]",
+          )
+        end
+
+        def has_dropdown_visible?
+          page.has_css?(".sidebar-hamburger-dropdown")
+        end
+
+        def has_no_dropdown_visible?
+          page.has_no_css?(".sidebar-hamburger-dropdown")
+        end
+
+        def visible?
+          page.has_css?(".hamburger-dropdown.header-dropdown-toggle")
+        end
+
+        def not_visible?
+          page.has_no_css?(".hamburger-dropdown.header-dropdown-toggle")
+        end
+
         def click_customize_community_section_button
           community_section.click_button(
             I18n.t("js.sidebar.sections.community.edit_section.header_dropdown"),
@@ -19,6 +50,16 @@ module PageObjects
 
           PageObjects::Modals::SidebarSectionForm.new
         end
+
+        private
+
+        def panel_id(panel)
+          if panel == "admin"
+            "admin-root"
+          elsif panel == "main"
+            "community"
+          end
+        end
       end
     end
   end

spec/system/page_objects/components/navigation_menu/sidebar.rb

@@ -9,6 +9,14 @@ module PageObjects
           wait_for_animation(find("div.menu-panel"))
         end
 
+        def click_header_toggle
+          find(header_toggle_css).click
+        end
+
+        def header_toggle_css
+          ".header-sidebar-toggle"
+        end
+
         def visible?
           page.has_css?("#d-sidebar")
         end