refactor(core): workbench (#7355)

Merge the right sidebar logic into the workbench. this can simplify our logic.

Previously we had 3 modules

* workbench
* right-sidebar (Control sidebar open&close)
* multi-tab-sidebar (Control tabs)

Now everything is managed in Workbench.

# Behavioral changes

The sidebar button is always visible and can be opened at any time.
If there is no content to display,  will be `No Selection`

![CleanShot 2024-06-28 at 14.00.41.png](https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/g3jz87HxbjOJpXV3FPT7/d74b3a60-2299-452e-877e-188186fe5ee5.png)

Elements in the sidebar can now be defined as`unmountOnInactive=false`. Inactive sidebars are marked with `display: none` but not unmount, so the `ChatPanel` can always remain in the DOM and user input will be retained even if the sidebar is closed.

packages/frontend/core/src/layouts/workspace-layout.tsx

@@ -47,6 +47,7 @@ import { SyncAwareness } from '../components/affine/awareness';
 import { appSidebarResizingAtom } from '../components/app-sidebar';
 import { usePageHelper } from '../components/blocksuite/block-suite-page-list/utils';
 import type { DraggableTitleCellData } from '../components/page-list';
+import { AIIsland } from '../components/pure/ai-island';
 import { RootAppSidebar } from '../components/root-app-sidebar';
 import { MainContainer } from '../components/workspace';
 import { WorkspaceUpgrade } from '../components/workspace-upgrade';
@@ -82,6 +83,7 @@ export const WorkspaceLayout = function WorkspaceLayout({
       <WorkspaceLayoutInner>{children}</WorkspaceLayoutInner>
       {/* should show after workspace loaded */}
       <WorkspaceAIOnboarding />
+      <AIIsland />
     </SWRConfigProvider>
   );
 };