Saving a post/page should also first save edited reusable blocks.

To reproduce:

1. On a page/post, edit a reusable block.
2. Forget to hit "save" on the reusable block.
3. Save the page/post.
4. Note that the reusable block edit is lost.

It seems expected behavior is that the edited reusable block would be automatically saved in the page/post Save.

Using 4.3.0.