Allow transitioning status from scheduled to draft

[earnjam]

Description

Modifies the PostSavedState component and the PostSwitchToDraftButton component to respect scheduled posts. This allows transitioning of posts from scheduled to draft without publishing first. Fixes #8327

How has this been tested?

Tested manually:

1. Create a new post
2. Set the date for sometime in the future.
3. Click Schedule
4. Switch to Draft button appears.
5. Optionally click Switch to Draft and get the alert to confirm unscheduling post, same as for unpublishing.
6. Change date to sometime in the past. Switch to Draft button remains as the alternative to Publish

Screenshots

Types of changes

Bug Fix
New Feature

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.

[jorgefilipecosta]

Code worked as expected in my tests and it looks good to me 👍