This basically reverts 9d4f79d3

Implemented by #22911
Related to #30677

I got this error in production using Puma in multi-threaded mode:

```
RuntimeError: Digest::Base cannot be directly inherited in Ruby
from active_support/security_utils.rb:23:in `variable_size_secure_compare'
from active_support/security_utils.rb:23:in `hexdigest'
from active_support/security_utils.rb:23:in `digest'
```

Looks like Digest uses const_missing to load Digest::SHA256 (https://github.com/ruby/ruby/blob/trunk/ext/digest/lib/digest.rb#L8)

- https://bugs.ruby-lang.org/issues/9494
- https://github.com/ruby/ruby/commit/c02fa39463a0c6bf698b01bc610135604aca2ff4

- Closes #30441

Currently `SchemaDumper` is only customizable for column options. But
3rd party connection adapters (oracle-enhanced etc) need to customizable
for table or index dumping also. To make it possible, I introduced
adapter specific `SchemaDumper` classes for that.

The limit option is ignored by PostgreSQL and may be ignored by 3rd
party backends.  Make this clear in the docs.  Fixes #29922.

This reverts commit 3420a145, reversing
changes made to afb66a5a.

`test_middleware_caches` is sometimes failed since #29454.
The failure is due to schema statements are affected by query caching.
Bypassing query caching for schema statements to avoid the issue.

Fixes #29460.

This option was added in b9fa3541. But it does not seem to work.

Use `SchemaMigration.all_versions` instead of
`SchemaMigration.all.map(&:version)` to avoid to instantiate AR objects.

Simply use `SchemaMigration.table_name` instead.

Related #25174.

`db:schema:load` doesn't work with subdirectories like previous
`db:migrate:status`. `Migrator.migration_files` should be used in
`assume_migrated_upto_version` to fix the issue.

Follow up of #26266.

The default type of `primary_key` and `references` were changed to
`bigint` since #26266. But `create_join_table` column type is still
`integer`. It should respect `references` column type.

The native timestamp type in MySQL is different from datetime type.
Internal representation of the timestamp type is UNIX time, This means
that timestamp columns are affected by time zone.

```
> SET time_zone = '+00:00';
Query OK, 0 rows affected (0.00 sec)

> INSERT INTO time_with_zone(ts,dt) VALUES (NOW(),NOW());
Query OK, 1 row affected (0.02 sec)

> SELECT * FROM time_with_zone;
+---------------------+---------------------+
| ts                  | dt                  |
+---------------------+---------------------+
| 2016-02-07 22:11:44 | 2016-02-07 22:11:44 |
+---------------------+---------------------+
1 row in set (0.00 sec)

> SET time_zone = '-08:00';
Query OK, 0 rows affected (0.00 sec)

> SELECT * FROM time_with_zone;
+---------------------+---------------------+
| ts                  | dt                  |
+---------------------+---------------------+
| 2016-02-07 14:11:44 | 2016-02-07 22:11:44 |
+---------------------+---------------------+
1 row in set (0.00 sec)
```

Extra `data_source_exists?(table_name)` is unneeded if
`drop_table(table_name, if_exists: true)` directly.

The `default` arg of `index_name_exists?` is only used the adapter does
not implemented `indexes`. But currently all adapters implemented
`indexes` (See #26688). Therefore the `default` arg is never used.

Closes #27979

Column options are passed as an hash args then used as `options` hash in
`add_column_options!`. Converting args to attributes is inconvinient for
using options as an hash.

Follow up to #26266.

The default type of `primary_key` and `references` were changed to
`bigint` since #26266. But legacy migration and sqlite3 adapter should
keep its previous behavior.

`ColumnDumper#migration_keys` was extracted to customize keys for
standardized column arguments widths. But the feature was removed in
df84e986. The internal method is no longer used for that.

These internal initialize methods are no longer used internally.

This reverts commit 39c77eb1, reversing
changes made to 9f6f51be.

Remove `initialize_schema_migrations_table` and `initialize_internal_metadata_table` internal public methods

These internal methods accidentally appeared in the doc, and so almost
useless. It is enough to create these internal tables directly, and
indeed do so in several places.

https://github.com/rails/rails/blob/v5.0.1/activerecord/lib/active_record/schema.rb#L55
https://github.com/rails/rails/blob/v5.0.1/activerecord/lib/active_record/railties/databases.rake#L6
https://github.com/rails/rails/blob/v5.0.1/activerecord/lib/active_record/tasks/database_tasks.rb#L230

Passing `name` to `tables` is already deprecated at #21601.
Passing `name` to `indexes` is also unused.