CPT: Enable restoring posts from post actions

[aduth]

Related: #6454

This pull request seeks to implement the behaviors related to restoring trashed posts from the custom post types list screen.

Testing instructions:

Verify that you can restore a trashed post.

1. Navigate to the custom post types list screen
2. If you don't already have a trashed post, trash one via the action dropdown
3. Change to the Trashed filter
4. For a trashed post, select Restore under the action menu
5. Note that...
   • The post disappears from the trashed list
   • The Trashed post count in the filter bar decrements by one
   • After the restore completes, the post count of the original status increments by one (we can't know until the response is received which status it was originally) and a notice is shown

Follow-up Tasks:

• Implement notices to reflect success or failure. I had planned to wait for State / CPT: Create notices middleware for observing actions #6645 to be merged before submitting this pull request, but discussion continues to evolve there, so would rather move forward with these changes. Included in 57da87d after having merged State / CPT: Create notices middleware for observing actions #6645.

Test live: https://calypso.live/?branch=update/cpt-restore-post

[codebykat]

This is working for me 👍

One quirk I noticed - if you Trash a published item, then restore it, it gets restored as a draft. I guess that's the API and/or core's fault though.

[codebykat]

The same sequence of events in wp-admin correctly restores the item as published. So I guess it's the API's fault...