feat: Add Essentials Toolbar

This commit introduces a new Essentials Toolbar feature to Zen. It provides a more streamlined and organized way for users to access frequently used bookmakrs directly from the sidebar.

- Added `ZenEssentialsToolbar.mjs` to provide the logic for the toolbar.
- Updated the sidebar CSS (`zen-sidebar.css`) to style the Essentials Toolbar.
- Modified `ZenStartup.mjs` to initialize the Essentials Toolbar.
- Made changes to `browserPlacesViews-js.patch` to integrate with existing bookmark functionality.
- Added a new preference `zen.essentials.enabled` to enable/disable the Essentials Toolbar.

src/browser/components/preferences/zen-settings.js

@@ -1099,5 +1099,10 @@ Preferences.addAll([
     id: "zen.view.compact.color-sidebar",
     type: "bool",
     default: true,
+  },
+  {
+  id: "zen.essentials.enabled",
+  type: "bool",
+  default: true,
   }
 ]);