Set changed time of an entity before validation runs to trigger EntityChangedConstraint consistently

So I dug into this quite a bit, and was surprised to see that the bug still exists on D11 and is actually much worse than it appears.

I wanted to see how Block Content worked since it doesn't have the same hidden changed field as Node (NodeForm adds this manually). I found out that the constraint isn't triggered at all for BlockContent because of this which could/should be considered data loss? Currently if I edit a block in 1 tab and then save the form again in another I don't get an error at all.

I think this should be fixed at the ContentEntityForm level. ::buildEntity is called before validation runs and we already set the revision changed time and other things in there. We could move the contents of ::updateChangedTime there as well and all entity types would benefit from this. We can then remove the hidden field from NodeForm.

Bumping to major because of the potential data loss.

xjm → credited catch → .

xjm → credited effulgentsia → .

xjm → credited star-szr → .

Crediting per major triage in #6.

xjm → credited alexpott → .