hippo:identifiable mixin is not "jackrabbit trivial", so cannot be applied during upgrade

The newly-introduced hippo:identifiable mixin defines a property hippo:identifier. This makes it "non-trivial" by Jackrabbit standards, so it cannot be upgraded automatically. This is an upgrade blocker, because it is now being used on the existing hst:containercomponent type. This causes bootstrapping to fail for any existing repository prior to 14.3.0.

IIUC, this could be worked around by separating the new property definition from the mixin. Adding a trivial mixin is BC, and adding a new, non-conflicting property to an existing node is BC, but combining the two is not BC.

The "proper fix" would be to make the Jackrabbit type system smarter by detecting when these two BC operations are combined via a non-trivial mixin, but that is likely overkill for this specific situation.

FYI, adouma aschrijvers.