Lock form should indicate if entity no longer locked.

Attaching static patch from current MR.

Attaching static patch after rebasing MR after latest release

Attaching a reroll of #15 for 3.0.0-alpha2.

Fixes an issue with the original #15 patch that causes error when the redirect Url generated from the destination parameter is not a routed Url (so the getRouteName() method can't be called on it). This can happen for example if the base path of the site contains a subdirectory, but there might be other cases when it's not possible to convert the destination parameter to a routed Url. This patch only uses the Url from the destination parameter to redirect if it's a routed Url, otherwise falls back to the entity canonical route.

Re #11: it seems that in this scenario the content is always locked. After breaking user B's lock, user A is redirected to content edit form, locking the content again (by user A). When user B visits the break lock form the content is locked by user A and user B doesn't have permission to unlock the content, so the access denied is technically correct. User B can only avoid the access denied (with this patch) if in the meantime user A also unlocks the content after breaking user B's lock.

The access denied in the scenario described in #11 could only be avoided if access is always allowed to the form and everything is handled in buildForm() with redirects, but not sure if that's the better solution.

Re-rolled the patch from #18 over the latest 3.0.0-alpha3 release.

Rebased the content of the previous MR and opened a new MR against 3.x since I was unable to change the target branch to 3.x.