Silence warning emitted in tests

[ci skip] Add missing prologue section of upgrading ruby on rails guide.

The instance method `model_name` was being defined multiple times,
causing a redefinition warning.

Fix doc unwanted dl Admin:: [ci skip]

Then we only need to extract host once.

Closes #15214

Since we are using both branches of the code is preferable to use
if/else over the early return.

Added String support for min and max properties for date field helpers

To avoid overload with database rollback

Added rollback method to ActiveModel::Dirty

Don't add a second method for attribute existence

We already had one in the public API that people can use more easily for
the transition

Fix 10.3 invite_email.body assert_match documentation example.

Currently there is no implicit conversion for Mail::Body to string
therefore .to_s must be applied. This is exampled in 10.2.2.

Update documentation on STI change handling

Documenting a potential source of confusion about how STI classes handle changes.

Simplify creation of default attributes on AR instance

Remove array workaround in PG quoting

Remove unused `array_member` from PG quoting for HStore columns

Hstore no longer needs additional quoting to be used in an array, the
array type handles it sufficiently.

We no longer need to do fancy legwork to make sure arrays use a type
object, now that schema methods use a real type object.

Use the type object when sending point columns to the DB

Don't encourage usage of `columns_hash`

Use `Hash#transform_values` to clean up `AttributeSet`

Use the type object for sending JSON to the database

`AttributeSet#dup` has all the behavior we need.

Add `Hash#map_values` to ActiveSupport to simplify a common pattern

Didn't get a chance to convert existing code, I'll skim through the code
base to make use of this later this afternoon.

As discussed in https://github.com/plataformatec/simple_form/pull/1094,
we should not encourage usage of `columns_hash`, and instead provide an
alternate method to determine whether or not an attribute exists.

The language `attribute` was chosen over `column` since these are in the
`AttributeMethods` module.

[ci skip]