feat(editor): viewport overlay widget extension (#12035)

Closes: BS-3360

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

- **New Features**
  - Introduced a new viewport overlay widget, making it available as part of the workspace and enabling its integration into supported pages.

- **Refactor**
  - Updated internal imports and exports to utilize the new viewport overlay widget package.
  - Streamlined widget registration and extension mechanisms for improved modularity.

- **Chores**
  - Added configuration and project references to support the new viewport overlay widget package in the build system.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/affine/widgets/viewport-overlay/src/effects.ts

@@ -0,0 +1,11 @@
+import {
+  AFFINE_VIEWPORT_OVERLAY_WIDGET,
+  AffineViewportOverlayWidget,
+} from './index';
+
+export function effects() {
+  customElements.define(
+    AFFINE_VIEWPORT_OVERLAY_WIDGET,
+    AffineViewportOverlayWidget
+  );
+}