refactor(editor): simplify TOC implementation with signal and context (#9873)

### What Changes
1. Used `@preact/signal` and `@lit/context` to simplify repetitive passing of properties of TOC components,
2. Fixed TOC invalid when editor changed, such as click new page button.

tests/kit/src/utils/page-logic.ts

@@ -199,6 +199,7 @@ export const dragTo = async (
 };
 
 // sometimes editor loses focus, this function is to focus the editor
+// FIXME: this function is not usable since the placeholder is not unstable
 export const focusInlineEditor = async (page: Page) => {
   await page
     .locator(