[web] Add a focus mode to the editor (#32245)

* Basic focus mode implementation

* Exit button

* Toggle between editor pdf mode

* Keep the rail and file tree mounted for editor tabs to work properly

* Hide Switch to editor button in focus mode

* Show shortcuts in layout menu

* Gate the feature behind a focus-mode feature flag

* Add split test badges in the focus mode dropdown item and top bar

* Add analytics tracking for focusMode changes

* Cleanup leftover IdeView value

* Allow passing focusMode value in layout test provider

* Remove redundant listener for focus mode shortcut

* Update focus mode and full project search listeners to use the event key

* Post-rebase cleanup

---------

Co-authored-by: Anna Fields <acfields11@gmail.com>
GitOrigin-RevId: 207f8d136fa6662558c474cca4a867a9842191e7

services/web/test/frontend/features/full-project-search/components/full-project-search.spec.tsx

@@ -98,6 +98,8 @@ const createInitialValue = () =>
     restoreView: cy.stub(),
     handleChangeLayout: cy.stub(),
     handleDetach: cy.stub(),
+    focusMode: false,
+    setFocusMode: cy.stub(),
   }) satisfies LayoutContextValue
 
 const LayoutProvider: FC<React.PropsWithChildren> = ({ children }) => {