fix(editor): behavior of deleting at the start of line (#12787)

Close BS-3182, #12736 




#### PR Dependency Tree


* **PR #12787** 👈

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

- **Bug Fixes**
- Improved the behavior when deleting empty lines and merging blocks,
ensuring more accurate handling of block deletion and cursor focus in
various scenarios.
- **Tests**
- Added new end-to-end tests to verify correct deletion of lines in
edgeless text and paragraph blocks, including checks for block removal
and cursor position.
- Introduced a utility function to retrieve block IDs for testing
purposes.

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

tests/blocksuite/e2e/edgeless/edgeless-text.spec.ts

@@ -11,6 +11,8 @@ import {
   edgelessCommonSetup,
   enterPlaygroundRoom,
   getEdgelessSelectedRect,
+  getIds,
+  getInlineSelectionIndex,
   getPageSnapshot,
   initEmptyEdgelessState,
   pasteByKeyboard,
@@ -21,6 +23,8 @@ import {
   pressBackspace,
   pressEnter,
   pressEscape,
+  pressShiftTab,
+  pressTab,
   redoByKeyboard,
   selectAllByKeyboard,
   setEdgelessTool,
@@ -552,6 +556,52 @@ test.describe('edgeless text block', () => {
       1
     );
   });
+
+  test('edgeless text should be able to delete line', async ({ page }) => {
+    await dblclickView(page, [100, -100]);
+    // 5: aaa
+    // 6:     bbb
+    // 7: ccc|
+    {
+      await type(page, 'aaa');
+      await pressEnter(page);
+      await pressTab(page);
+      await type(page, 'bbb');
+      await pressEnter(page);
+      await pressShiftTab(page);
+      await type(page, 'ccc');
+    }
+
+    // 5: aaa
+    // 6:     bbb|
+    await pressBackspace(page, 4);
+    expect(await getIds(page)).not.toContain(7);
+    await assertBlockTextContent(page, 5, 'aaa');
+    await assertBlockTextContent(page, 6, 'bbb');
+    expect(await getInlineSelectionIndex(page)).toBe(3);
+
+    // 5: |aaa
+    // 6:     bbb
+    {
+      await pressArrowUp(page);
+      await pressArrowLeft(page, 3);
+      await pressBackspace(page);
+    }
+
+    await assertBlockTextContent(page, 5, 'aaa');
+    await assertBlockTextContent(page, 6, 'bbb');
+    expect(await getInlineSelectionIndex(page)).toBe(0);
+
+    // 6: |bbb
+    {
+      await pressArrowRight(page, 3);
+      await pressBackspace(page, 4);
+    }
+
+    expect(await getIds(page)).not.toContain(7);
+    await assertBlockTextContent(page, 6, 'bbb');
+    expect(await getInlineSelectionIndex(page)).toBe(0);
+  });
 });
 
 test('press backspace at the start of first line when edgeless text exist', async ({