Closes #18664.

This is a backport of:

* 174f5ed5 add test to ensure `remove_reference` with index and fk is invertable. [Yves Senn]
* a893718c fix `remove_reference` with `foreign_key: true` on MySQL. #18664. [Yves Senn]
* e550bbf8 Changelog for 99a6f9e6 [Sean Griffin]
* 84927431 Don't wrap `create_table` in a transaction for tests which run on MySQL [Sean Griffin]
* b7d7e0b1 Add test missed by a03ea684 [Sean Griffin]
* a03ea684 Use the new `foreign_key` option on `references` in generators [Sean Griffin]
* 82afeaf2 Add `foreign_key` as an option to `references` for `change_table` [Sean Griffin]
* 99a6f9e6 Add a `foreign_key` option to `references` while creating the table [Sean Griffin]

=====================================================

Rather than having to do:

    create_table :posts do |t|
      t.references :user
    end

    add_foreign_key :posts, :users

You can instead do:

    create_table :posts do |t|
      t.references :user, foreign_key: true
    end

Similar to the `index` option, you can also pass a hash. This will be
passed as the options to `add_foreign_key`. e.g.:

    create_table :posts do |t|
      t.references :user, foreign_key: { primary_key: :other_id }
    end

is equivalent to

    create_table :posts do |t|
      t.references :user
    end

    add_foreign_key :posts, :users, primary_key: :other_id