It's become clear to me that the use case is still a bit muddy
and the upgrade path is going to be tough for people to figure
out.

This attempts at understanding it better through documentation,
but still needs follow up work.

[ Michael Coyne & Kasper Timm Hansen ]

[ Michael Coyne & Kasper Timm Hansen ]

Noticed that verifiers and encryptors never once mentioned key generators
and salts but only concerned themselves with generated secrets.

Clears up the confusing naming around raw_key and secret as well. And
makes the rotation API follow the constructor signature to the letter.

Spares users from passing in non-changing values explicitly.

[ Michael Coyne & Kasper Timm Hansen ]

Add Key Rotation to MessageEncryptor and MessageVerifier and simplify the Cookies middleware

Update Action Mailer Basics [ci skip]

Using the action_dispatch.cookies_rotations interface, key rotation is
now possible with cookies. Thus the secret_key_base as well as salts,
ciphers, and digests, can be rotated without expiring sessions.

Fix rails middleware list in api_app guide [ci skip]

Fix email in Active Support Instrumentation [ci skip]

* `s/ddh/dhh/`

Both classes now have a rotate method where new instances are added for
each call. When decryption or verification fails the next rotation
instance is tried.

* `MyApi::Application::Routes` is not middleware.

Make bang version work with `InheritableOptions`

Currently, bang version does not work with `InheritableOptions`.
`InheritableOptions` treats the argument Hash as the default value.
However, `Hash#fetch` does not use the default value when key is not
found, so can not get the default value.
So in bang version, should use `Hash#[]` instead of `Hash#fetch`.

Currently the normalization only exists in `primary_key` shorthand. It
should be moved to `new_column_definition` to also affect to
`add_column` with primary key.

Currently implicit legacy primary key is compatible, but adding explicit
legacy primary key is not compatible. It should also be fixed.

Fixes #30664.

Ensure `1 AS one` for SQL Server with Calculations

`change_column_{default,null,comment}` in mysql2 adapter are passing
`column.sql_type` as `type` to `change_column` to intend keeping
previous type. But `column_for` requires extra query, so use passing
`nil` to `type` explicitly in the internal for the purpose.

Implement change_table_comment and change_column_comment

Use `TOPLEVEL_BINDING` in rails runner command

Binding to capture the local scope. This means that if a constant with same
name as constant specified by the user exists in local scope, constant
defined in local will use. This is different from what the user expects.
Therefore, fixed to use top-level binding instead of local scope.

Fixes #30644

Use algorithm while removing index with db:rollback

Fix "warning: `*' interpreted as argument prefix"

Closes #24190

This fixes following warning:

```
/home/travis/build/rails/rails/activerecord/test/cases/instrumentation_test.rb:11: warning: `*' interpreted as argument prefix
/home/travis/build/rails/rails/activerecord/test/cases/instrumentation_test.rb:23: warning: `*' interpreted as argument prefix
/home/travis/build/rails/rails/activerecord/test/cases/instrumentation_test.rb:35: warning: `*' interpreted as argument prefix
/home/travis/build/rails/rails/activerecord/test/cases/instrumentation_test.rb:48: warning: `*' interpreted as argument prefix
/home/travis/build/rails/rails/activerecord/test/cases/instrumentation_test.rb:61: warning: `*' interpreted as argument prefix
```

Update link in The Asset Pipeline guide [ci skip]

Update payload names for `sql.active_record` instrumentation to be more descriptive.

Update Rails Guides about  :autosave option

Fixes #30586.