to "without replacement"

We've stopped using it internally, in favor of polymorphism. So should
you!

Fixes #15705.

This fixes #15496

member = Member.new(club: Club.new)
member.save!

Before:

member.current_membership.club_id # => nil

After:

member.current_membership.club_id # => club's id

We have several mutable types on Active Record now. (Serialized, JSON,
HStore). We need to be able to detect if these have been modified in
place.

We always define attribute methods in the constructor or in `init_with`.

variables [ci skip]
Thanks to @matthewd for the excellent feedback! ❤

We don't generally modify our classes at runtime like this. Let's create
the instance after the class is created. Original commit doesn't imply
that this was intentional behavior.

This partially reverts commit 1a203d5e.

Reason: It was committed by accident

There's a lot more that can be moved to these, but this felt like a good
place to introduce the object. Plans are:

- Remove all knowledge of type casting from the columns, beyond a
  reference to the cast_type
- Move type_cast_for_database to these objects
- Potentially make them mutable, introduce a state machine, and have
  dirty checking handled here as well
- Move `attribute`, `decorate_attribute`, and anything else that
  modifies types to mess with this object, not the columns hash
- Introduce a collection object to manage these, reduce allocations, and
  not require serializing the types

We guarantee that `model.value` does not change after
`model.save && model.reload`. This requires type casting user input for
non-string types.

We'd spend a lot of time calling `hash` and `eql?` on the join model,
which has no primary key. Calling `id` with no primary key is a really
slow way to get back `nil`, so we can improve the performance there.
However, even with the escape clause, we *still* weren't getting high
enough performance, as we were checking the primary key too much. `hash`
will always return `nil.hash` for records with no id, and `==` will
always return `false`. We can optimize those cases in the HABTM join
model.

Topics call `serialize :content`, which means that the values in the
database should be YAML encoded, and we would only expect to receive
YAML strings to `update_column` and `update_columns`.

Additionally:
* It changes `purge` task on `sqlite3` adapter to recreate database file, to
be consistent with other adapters.
* Adds `purge` step when loading from `schema.rb`

The column name given by the adapter doesn't include the table
namespace, so going through the hashed version of the result set causes
overridden keys.

Fixes #15649

We're not longer using `ipaddr` in schema dumper

The original patch that added this concept can be found
[here](https://web.archive.org/web/20090601022739/http://dev.rubyonrails.org/ticket/9767).
The current default behavior is to cache everything except serialized
columns, unless the user specified otherwise. If anyone were to specify
otherwise, many types would actually be completely broken. Still, the
method is left in place with a deprecation warning in case anyone is
actually still calling this method.

We are no longer including column objects in YAML serialization, thanks
to https://github.com/rails/rails/pull/15621

use name specified by 'as' for automatic inverse association to avoid reflecting on wrong association

add_constraints is complicated and difficult to read. This is the
beginning of a long process of refactoring this code. First step:
moved the join keys out of AssociationScope and into reflection.

We then don't need to call `reflection` because now reflection is
`self`.

`foreign_key` must be named something else because reflection already has a
`foreign_key` method and when passed into `JoinKeys` it was getting the
wrong assignment. `reflection_foreign_key` seemed to be an appropriate name.
I also named `key` `reflection_key` to match `reflection_foreign_key`.

We never want result types to override column types, and
`decorate_columns` can only affect column types. No need to go through
the decoration multiple times, we can just exclude the column types from
the result types instead.

```
activerecord/test/cases/adapters/postgresql/range_test.rb:159: warning: (...) interpreted as grouped expression
activerecord/test/cases/finder_test.rb:38: warning: shadowing outer local variable - e
activerecord/test/cases/finder_test.rb:43: warning: shadowing outer local variable - e
```

On MySQL and PostgreSQL, the adapter does not type cast virtual columns
for us.