perf(editor): fallback to placeholder for canvas text (#12033)

### TL;DR

For canvas elements, this PR adds placeholders during zooming operations to improve performance.

![image.png](https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/lEGcysB4lFTEbCwZ8jMv/8c8daea8-1eb4-419b-a4f4-2a8847f40b7b.png)

### What changed?

- Implemented placeholder rendering during zooming operations in the canvas renderer, but not only DOM.
- Added a `forceFullRender` property to the `GfxCompatibleInterface` to allow elements to opt out of placeholder rendering
- Set `forceFullRender = true` for connectors to ensure they always render properly, even during zooming
- Connected the turbo renderer to the viewport's zooming state to automatically switch between full and placeholder rendering

### Why make this change?

Rendering complex elements during zooming operations can cause performance issues and make the UI feel sluggish. Rendering connector label also leads to high cost DOM `set font` delays.

![image.png](https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/lEGcysB4lFTEbCwZ8jMv/961fb847-24b4-4a7f-b9dc-21b0a5edaaa1.png)

The turbo renderer improves performance by displaying simple placeholders for elements during zooming, while still rendering critical elements like connectors fully. This creates a smoother user experience while maintaining essential visual information.

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

## Summary by CodeRabbit

- **New Features**
  - Introduced a feature-flag-controlled "turbo" rendering mode that displays placeholder graphics during zooming for improved performance.
  - Added the ability to override placeholder rendering for specific elements, ensuring full rendering when required.

- **Bug Fixes**
  - Enhanced rendering logic to ensure connectors always render fully, even during zoom operations.

- **Documentation**
  - Updated API documentation to reflect new properties related to rendering behavior.

- **Tests**
  - Improved tests to verify correct rendering behavior for connectors.

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

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

@@ -19,6 +19,7 @@ export interface BlockSuiteFlags {
   enable_callout: boolean;
   enable_edgeless_scribbled_style: boolean;
   enable_embed_doc_with_alias: boolean;
+  enable_turbo_renderer: boolean;
 }
 
 export class FeatureFlagService extends StoreExtension {
@@ -42,6 +43,7 @@ export class FeatureFlagService extends StoreExtension {
     enable_callout: false,
     enable_edgeless_scribbled_style: false,
     enable_embed_doc_with_alias: false,
+    enable_turbo_renderer: false,
   });
 
   setFlag(key: keyof BlockSuiteFlags, value: boolean) {