fix(editor): edgeless note duplicated from embed-doc should be above other elements (#12028)

Close [BS-3357](https://linear.app/affine-design/issue/BS-3357/duplicate-note-注意设置z轴的数据)

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

## Summary by CodeRabbit

- **New Features**
  - Duplicating an edgeless note now ensures the new note appears above other elements in the stacking order.

- **Tests**
  - Added a test to verify that duplicated edgeless notes are rendered above existing elements.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/affine/blocks/embed/src/embed-synced-doc-block/configs/toolbar.ts

@@ -375,6 +375,7 @@ const builtinSurfaceToolbarConfig = {
                     DEFAULT_NOTE_WIDTH,
                     DEFAULT_NOTE_HEIGHT
                   ).serialize(),
+                  index: gfx.layer.generateIndex(),
                   displayMode: NoteDisplayMode.EdgelessOnly,
                 } satisfies Partial<NoteProps>,
                 ctx.store.root