PLAT-235 paragraph constraint issue

[pvhee]

Fixes https://jira.comicrelief.com/browse/PLAT-235

Changes proposed in this pull request

• Applies core patch (see makefile)
• Write tests for landign page adding/editing

Reasoning behind this

As reported in https://jira.comicrelief.com/browse/PLAT-235, we have a problem editing a node that contains paragraphs, as it returns an EntityChangedConstraint (text reads like The content has either been modified by another user, or you have already submitted modifications. As a result, your changes cannot be saved.).

From EntityChangedConstraintValidator, this happens when the changed time of the updated entity is lower then the changed time of the entity to be updated, meaning that a user is likely to change an entity that has been changed in the meantime.

This makes a lot of sense for nodes, but somehow gets messed up for paragraph entities that should not have an updated date (they belong to the host entity!). This has been reported and supposedly fixed for paragraphs in https://www.drupal.org/node/2715855, but applying this patch leads to a new issue: This entity (paragraph: ) cannot be referenced `, which has been reported in https://www.drupal.org/node/2724243 (set to critical) and for which currently (May 18th) no solution exists.

Hence the reason to apply a core patch to remove this constraint for paragraphs. It should be harmless, and can be removed once the solution is properly fixed in paragraphs.

[pvhee]

@wagg-matt do you think you could look at writing some tests for creating landing pages including row components if not yet on your radar? I got stuck on finding the right buttons to click to add these row components, let's chat to find out how we can solve this.

[wagg-matt]

@pvhee sure thing, is all code in this PR?

[pvhee]

@bimsonz rev & merge pls? not nice, but the reasoning is explained on top

[bimsonz]

@pvhee only option for now really, looks good! lets change the ticket to a watch ticket and move to blocked and keep an eye on the issue, i want to look into updating paragraphs as that and ERR might have had some updates.