Show reason for foreign key error when loading fixtures

[ghiculescu]

#42674 added the ability to have Rails verify foreign keys when creating fixtures. Feedback from users since then is it would be handy to know which foreign keys are being violated. See #44943 and #47780 for attempts to fix this.

This PR rolls up some of the ideas from those PRs into one that's hopefully mergable.

• all_foreign_keys_valid? is deprecated in favour of check_all_foreign_keys_valid!.
• Postgres and Sqlite adapters raise an error with detail about the foreign key error.
• Authors of other PRs added as co-authors here to get credit.
• Deprecations updated to work with new deprecation APIs.
• Tests updated.

Here's what the error messages will now look like.

Postgres:

Foreign key violations found in your fixture data. Ensure you aren't referring to labels that don't exist on associations. Error from database:

PG::ForeignKeyViolation: ERROR:  insert or update on table "fk_pointing_to_non_existent_objects" violates foreign key constraint "fk_that_will_be_broken"
DETAIL:  Key (fk_object_to_point_to_id)=(980190962) is not present in table "fk_object_to_point_tos".
CONTEXT:  SQL statement "UPDATE pg_constraint SET convalidated=false WHERE conname = 'fk_that_will_be_broken' AND connamespace::regnamespace = 'public'::regnamespace; ALTER TABLE public.fk_pointing_to_non_existent_objects VALIDATE CONSTRAINT fk_that_will_be_broken;"
PL/pgSQL function inline_code_block line 16 at EXECUTE

Sqlite:

Foreign key violations found in your fixture data. Ensure you aren't referring to labels that don't exist on associations. Error from database:

Foreign key violations found: fk_pointing_to_non_existent_objects

Closes #47780
Closes #44943

cc @s-mage @danini-the-panini

[byroot]

If there is no more concerns I can merge.

[ghiculescu]

@byroot I think we should merge it. I've made a PR for https://github.com/jruby/activerecord-jdbc-adapter, see jruby/activerecord-jdbc-adapter#1129.

It doesn't seem like https://github.com/rsim/oracle-enhanced has implemented the relevant method, nor has https://github.com/rails-sqlserver/activerecord-sqlserver-adapter. I don't know of any other popular adapters, but happy to reach out to (or make PRs for) any others worth checking.

[yahonda]

Thanks for the work.