V13: Move publishing notification after validation

[Zeegaan]

Notes

• Implements suggestion from: ContentPublishingNotification is published to early - inconsistency during publishing #14034
• In short: Publishing notification was fired before validation, this has now been moved to afterwards. (As we only want to publish valid content)

How to test

• Follow steps from discussion

[Migaroez]

Solves the issue/discussion as advertised.

Had some concerns about functional changes but the magic Success based on the bit value of the OperationStatuses seems to take it all into account 👍

[nzdev]

With this pr in place, if the content is changed during ContentPublishingNotification, the content is left in Published (Pending Changes) state. E.g. if you want to set a field value at the time of publishing (e.g. a record of when the content was first published) it now shows no extra current version created and Published (Pending Changes) state which is a breaking change.

[markadrake]

@Zeegaan, @Migaroez,
Would you kindly review @nzdev's opened issue: #17023.
This is indeed a breaking change.
Very quick/easy to replicate.