Unlike other databases, changing SQLite3 table definitions need to create a temporary table.
While changing table operations, the original table needs dropped which caused
`SQLite3::ConstraintException: FOREIGN KEY constraint failed` if the table is referenced by foreign keys.
This pull request disables foreign keys by `disable_referential_integrity`.

Also `disable_referential_integrity` method needs to execute `defer_foreign_keys = ON`
to defer re-enabling foreign keys until the transaction is committed.

https://www.sqlite.org/pragma.html#pragma_defer_foreign_keys

Fixes #31988

- This `defer_foreign_keys = ON` has been supported since SQLite 3.8.0
https://www.sqlite.org/releaselog/3_8_0.html and Rails 6 requires SQLite 3.8 #32923 now

- <Models>.reset_column_information added to address `ActiveModel::UnknownAttributeError`

```
Error:
ActiveRecord::Migration::ForeignKeyChangeColumnTest#test_change_column_of_parent_table:
ActiveModel::UnknownAttributeError: unknown attribute 'name' for ActiveRecord::Migration::ForeignKeyChangeColumnTest::Post.
```

Bump minimum SQLite version to 3.8

To prevent redundant `to_s` like https://github.com/rails/rails/pull/32923#discussion_r189460008
automatically in the future.

These OS versions have SQLite 3.8 or higher by default.

- macOS 10.10 (Yosemite) or higher
- Ubuntu 14.04 LTS or higher

Raising the minimum version of SQLite 3.8 introduces these changes:

- All of bundled adapters support `supports_multi_insert?`
- SQLite 3.8 always satisifies `supports_foreign_keys_in_create?` and `supports_partial_index?`
- sqlite adapter can support `alter_table` method for foreign key referenced tables by #32865
- Deprecated `supports_multi_insert?` method

So do not expose `PostgreSQLTypeMetadata` in the doc too.

Follow up of #32418.

Finalize transaction record state after real transaction

After a real (non-savepoint) transaction has committed or rolled back,
the original persistence-related state for all records modified in that
transaction is discarded or restored, respectively.

When the model has transactional callbacks, this happens synchronously
in the `committed!` or `rolled_back!` methods; otherwise, it happens
lazily the next time the record's persistence-related state is accessed.

The synchronous code path always finalizes the state of the record, but
the lazy code path only pops one "level" from the transaction counter,
assuming it will always reach zero immediately after a real transaction.
As the test cases included here demonstrate, that isn't always the case.

By using the same logic as the synchronous code path, we ensure that the
record's state is always updated after a real transaction has finished.

Don't generate yarn's contents in `app:update` task if it's skipped

Fix documentation for ActionController::Params#fetch

Fixes #32928.

Make it clear that the return value is converted to an
instance of ActionController::Parameters if possible

Generate ActiveStorage attachment getter and setter methods in mixin

Generated attachment getter and setter methods are created within
the model's `GeneratedAssociationMethods` module to allow overriding
and composition using `super`.

Includes tests for new functionality.
Co-authored-by: NJosh Susser <josh@hasmanythrough.com>
Co-authored-by: NJamon Douglas <terrildouglas@gmail.com>

Fix user_input_in_time_zone to coerce non valid string into nil

Active storage: Image variant options not correct in docs

[ci skip]

### Steps to reproduce

Using Rails 5.2.0

When following this example:

http://api.rubyonrails.org/classes/ActiveStorage/Variant.html

`avatar.variant(resize: "100x100", monochrome: true, flip: "-90")`

### Expected behavior

Image should be rendered as flipped.

### Actual behavior

I get an error:

> failed with error: gm mogrify: Unrecognized option (-90).

### Fix:

According to: https://github.com/minimagick/minimagick the option should be called rotate:

`avatar.variant(resize: "100x100", monochrome: true, rotate: "-90")`

So **flip** changed to **rotate**.

### System configuration
**Rails version**: 5.2.0

**Ruby version**: ruby 2.5.1p57 (2018-03-29 revision 63029) [x86_64-darwin17]

[David Robertson & George Claghorn]

Before it was coercing an invalid string into "2000-01-01 00:00:00".

Inside user_input_in_time_zone we call in_time_zone on the value and value can be a String.

Originally `SingularAssociation#replace` abstract method is private, and
doesn't intend to be called directly.

Follow up of #19171 and #26825.

Add math test

After #449 was merged math can be done on these
nodes, adding a test file to unit test all the
math operators.

Don't generate `config/spring.rb` in `app:update` task when spring isn't loaded

Add available transformations to docs

`foreign_key`, `json` and `virtual` are also available.

Follow up of #32605.

Remove ActiveRecord::Transactions#rollback_active_record_state!

Don't clear transaction state after manual rollback