feat(editor): flat block data (#9854)

Flat block data.

A new block type to flatten the block data

```typescript
// For developers
type Model = {
  blocks: Record<string, {
    flavour: string;
    cells: Record<string, {
      rowId: string;
      colId: string;
      text: Text;
    }>;
    cols: Record<string, {
      align: string;
    }>
    rows: Record<string, {
      backgroundColor: string;
    }>
  }>
}

// How it's saved in yjs
const yData = {
  blocks: {
    'blockId1': {
      flavour: 'affine:table',
      'prop:rows:row1:backgroundColor': 'white',
      'prop:cols:col1:align': 'left',
      'prop:cells:cell1:rowId': 'row1',
      'prop:cells:cell1:colId': 'col1',
      'prop:cells:cell1:text': YText,
      prop:children: []
    },
  }
}
```

blocksuite/framework/store/src/transformer/json.ts

@@ -1,6 +1,6 @@
 import { NATIVE_UNIQ_IDENTIFIER, TEXT_UNIQ_IDENTIFIER } from '../consts';
+import { isPureObject } from '../reactive';
 import { Boxed } from '../reactive/boxed';
-import { isPureObject } from '../reactive/index';
 import { Text } from '../reactive/text';
 
 export function toJSON(value: unknown): unknown {