feat(editor): by default render code iframe for html preview (#12848)

#### PR Dependency Tree


* **PR #12848** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

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

- **New Features**
- Introduced a feature flag to enable or disable web container
functionality for code block previews.
- **Improvements**
- Code block HTML previews now support an alternative rendering method
based on the new feature flag, enhancing flexibility.
- **Chores**
- Updated feature flag settings by removing an obsolete flag and adding
the new web container flag.
- **Tests**
- Simplified code block preview tests for faster and more direct
validation of HTML preview content.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

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

@@ -21,6 +21,7 @@ export interface BlockSuiteFlags {
   enable_table_virtual_scroll: boolean;
   enable_turbo_renderer: boolean;
   enable_dom_renderer: boolean;
+  enable_web_container: boolean;
 }
 
 export class FeatureFlagService extends StoreExtension {
@@ -46,6 +47,7 @@ export class FeatureFlagService extends StoreExtension {
     enable_table_virtual_scroll: false,
     enable_turbo_renderer: false,
     enable_dom_renderer: false,
+    enable_web_container: false,
   });
 
   setFlag(key: keyof BlockSuiteFlags, value: boolean) {