Fix reverting the addition of invalid foreign keys and check constraints

[fatkodima]

Adding foreign keys and check constraints to an existing (large) table is dangerous in PostgreSQL, because they need to be checked (validated) and while they are validated, the table stays exclusively locked. So, usually, they are added as invalid and then validated in a separate transaction.

Something like:

class AddForeignKeyFromRepositoriesToUsers < ActiveRecord::Migration[7.1]
  disable_ddl_transaction!

  def change
    add_foreign_key :repositories, :users, validate: false
    validate_foreign_key :repositories, :users
  end
end

This migration is reversible, because of the bug in

rails/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb

Line 143 in a2fc96a

(validate.nil? || validate == options.fetch(:validate, validate)) &&

Note the missing self in options.fetch....

Similar migration was also always reversible before #45808 (because before that PR, only name was checked for check constraints to match the searched one).

So, this PR fixes defined_for? for both foreign keys and check constraints to work correctly with validity and makes adding them them as invalid a reversible operation.