Fix discard draft loosing all changes

[yaelirub]

When a post fails to save, it status was set to AbstractPostRemoteStatusFailed which should have
made post.hasNeverAttemptedToUpload return true hence return false in shouldRemovePostOnDismiss in discardChanges().

WordPress-iOS/WordPress/Classes/ViewRelated/Post/PostEditor+Publish.swift

Line 239 in d05cb73

let shouldRemovePostOnDismiss = post.hasNeverAttemptedToUpload() && !post.isLocalRevision

The problem was that the remoteStatus property was not really being saved. In order to save those changes we are merging the revisions back into the base post.

Fixes #11435

To test:

upload failed post with no changes

1.Be offline
2.Create a new draft
3.Save draft (either through options menu or by exiting the editor and choosing "save draft")
4.rerun xcode
5.See the post with "failed upload" status
6.tap on post
7.Exist editor
8.Choose discard
*Expected - post is not be deleted.

upload failed post with changes:

1.Follow steps 1-6 above
2.Make changes to post
3.Exit editor
4.Choose discard
Expected - Changes made in step 2 will be discarded and the post is not be deleted.
Before:

After:

Update release notes:

If there are user facing changes, I have added an item to RELEASE-NOTES.txt.

[jklausa]

This took me a while to wrap my head around why this was needed!

I... really dislike that we're doing [NSManagedObjectContext performBlock:] inside a network callback, but the success block was doing it already anyway, so ¯_(ツ)_/¯.

Great job tracking this down and fixing it!

[yaelirub]

Thanks, @jklausa!

really dislike that we're doing [NSManagedObjectContext performBlock:] inside a network callback

I see your point. Hopefully the implementation of uploads manager will separate the network call from saving locally. At least for uploading