[Bug] Turning a Page block into another type of block results in the page's contents disappearing

### Bug Description

Using any type of "turn into" on a page block makes the page contents disappear.

This is similar to issues #7585 and #7586 that I opened before, but this case is not related to undoing or using a shortcut.

### How to Reproduce

1) Create a page using /document
2) Add title and content
3) Return to the parent page
4) Use "turn into" to change the page block into something else
5) The page contents disappear, only its title is transformed

### Expected Behavior

Turning a page into other types should make the title into that type and put the page contents below it.

If the new type supports it (like text and Toggle types) add a level of indentation or put the content inside the block.

### Operating System

Windows 10

### AppFlowy Version(s)

0.8.7

### Screenshots

_No response_

### Additional Context

_No response_