fix(editor): virtual keyboard closes unexpectedly when backspace is pressed after a block (#13386)

Close
[AF-2764](https://linear.app/affine-design/issue/AF-2764/移动端没法删除图片和其他非文本block)

#### PR Dependency Tree


* **PR #13386** 👈

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

* **New Features**
* Improved virtual keyboard handling on mobile devices to prevent
unexpected keyboard closure during certain editing actions.
* Added new signals for keyboard height and safe area, enhancing UI
responsiveness and adaptability to keyboard state.

* **Refactor**
* Streamlined keyboard toolbar logic for more reliable panel height
calculation and smoother panel open/close transitions.
* Simplified and modernized the approach to toolbar visibility and input
mode restoration.

* **Style**
* Updated keyboard toolbar and panel styling for better positioning and
layout consistency across devices.

* **Bug Fixes**
* Fixed an issue where the virtual keyboard could be incorrectly
reported as visible when a physical keyboard is connected.

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

blocksuite/affine/blocks/paragraph/src/utils/merge-with-prev.ts

@@ -24,6 +24,7 @@ import {
   getPrevContentBlock,
   matchModels,
 } from '@blocksuite/affine-shared/utils';
+import { IS_MOBILE } from '@blocksuite/global/env';
 import { BlockSelection, type EditorHost } from '@blocksuite/std';
 import type { BlockModel, Text } from '@blocksuite/store';
 
@@ -91,10 +92,17 @@ export function mergeWithPrev(editorHost: EditorHost, model: BlockModel) {
       ...EMBED_BLOCK_MODEL_LIST,
     ])
   ) {
-    const selection = editorHost.selection.create(BlockSelection, {
-      blockId: prevBlock.id,
-    });
-    editorHost.selection.setGroup('note', [selection]);
+    // due to create a block selection will clear text selection, which lead
+    // the virtual keyboard to be auto closed on mobile. This behavior breaks
+    // the user experience.
+    if (!IS_MOBILE) {
+      const selection = editorHost.selection.create(BlockSelection, {
+        blockId: prevBlock.id,
+      });
+      editorHost.selection.setGroup('note', [selection]);
+    } else {
+      doc.deleteBlock(prevBlock);
+    }
 
     if (model.text?.length === 0) {
       doc.deleteBlock(model, {