column-level unique constraints

[gavinking]

Late to the party, I suppose (10 years ago!), but I disagree with the resolution of: HHH-7797

It seems to me that alter table is by far the ugliest way to create unique constraints (especially with the nasty generated names we use), and yet apparently that's the method we prefer and almost always use.

I see that the justification for this change at the time was that the existing logic was a bit wrong or difficult to follow, or something, but that just sounds like a pretty lazy justification, especially since the basic plumbing seems to be there in UniqueDelegate, and we just seem to not be taking advantage of it.

I would reverse the order of preference that is documented by UniqueDelegate, and change DefaultUniqueDelegate to implement the new priority.

[gavinking]

This change is done.

[gavinking]

See https://hibernate.atlassian.net/browse/HHH-15762 for further discussion of this.