feat(editor): edgeless page block toolbar (#9707)

Close [BS-2315](https://linear.app/affine-design/issue/BS-2315/page-block-header)

### What Changes
- Add header toolbar to page block (the first note in canvas)
- Add e2e tests
- Add some edgeless e2e test utils.  **The package `@blocksuite/affine` was added to `"@affine-test/kit"`**

blocksuite/affine/shared/src/services/feature-flag-service.ts

@@ -18,6 +18,7 @@ export interface BlockSuiteFlags {
   enable_shape_shadow_blur: boolean;
   enable_mobile_keyboard_toolbar: boolean;
   enable_mobile_linked_doc_menu: boolean;
+  enable_page_block_header: boolean;
 }
 
 export class FeatureFlagService extends StoreExtension {
@@ -40,6 +41,7 @@ export class FeatureFlagService extends StoreExtension {
     enable_shape_shadow_blur: false,
     enable_mobile_keyboard_toolbar: false,
     enable_mobile_linked_doc_menu: false,
+    enable_page_block_header: false,
   });
 
   setFlag(key: keyof BlockSuiteFlags, value: boolean) {