feat(editor): use affine container url in preview (#12919)

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

- **Bug Fixes**
- Improved code block preview rendering to only display the preview when
appropriate, preventing unwanted previews.

- **Refactor**
- Simplified the HTML preview system by always using a secure
iframe-based approach and removing the WebContainer integration.
- Updated iframe permissions and content delivery for enhanced security
and compatibility.

- **Chores**
- Removed the "Enable Web Container" feature flag and all related
internal logic.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/affine/blocks/code/src/code-block.ts

@@ -450,7 +450,7 @@ export class CodeBlockComponent extends CaptionedBlockComponent<CodeBlockModel>
           contenteditable="false"
           class="affine-code-block-preview"
         >
-          ${previewContext?.renderer(this.model)}
+          ${shouldRenderPreview && previewContext?.renderer(this.model)}
         </div>
         ${this.renderChildren(this.model)} ${Object.values(this.widgets)}
       </div>