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/editor.ts

@@ -52,6 +52,14 @@ export function locateEditorContainer(page: Page, editorIndex = 0) {
   return page.locator('[data-affine-editor-container]').nth(editorIndex);
 }
 
+export function locateDocTitle(page: Page, editorIndex = 0) {
+  return locateEditorContainer(page, editorIndex).locator('doc-title');
+}
+
+export async function focusDocTitle(page: Page, editorIndex = 0) {
+  await locateDocTitle(page, editorIndex).locator('.inline-editor').focus();
+}
+
 // ================== Page ==================
 export function locateFormatBar(page: Page, editorIndex = 0) {
   return locateEditorContainer(page, editorIndex).locator(

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(