Remove deprecated methods `initialize_schema_migrations_table` and `initialize_internal_metadata_table`

It should be shared the count of alias tracking in both INNER/LEFT JOINs
to avoid duplicate aliases.

Fixes #30504.
Closes #30410.

Currently we have no test for alias tracking with string joins. I've add
test case for that to catch a future regression.

Since `MocktailDesigner` inherits `DrinkDesigner` and can not be used
alone.

This basically reverts 9d4f79d3

It should be initialized only when polymorphic associations.

Enable `hstore` extention disabled at the end of `InvertibleMigrationTest#test_migrate_enable_and_disable_extension`
to avoid failure of `PostgresqlArrayTest#test_schema_dump_with_shorthand`
which expects `hstore` extension enabled.

Passing `true` to force an association to reload its records from the
database was deprecated in 5.0 and removed in 5.1.

  When load schema from `structure.sql`, database connection isn't
  established. `ActiveRecord::Tasks::DatabaseTasks.load_schema` has to
  establish database connection since it executes
  ```
  ActiveRecord::InternalMetadata.create_table
  ActiveRecord::InternalMetadata[:environment] = environment
  ```

Fix `bin/rails db:setup` and `bin/rails db:test:prepare` create  wrong ar_internal_metadata's data for a test database.

  Before:
  ```
  $ RAILS_ENV=test rails dbconsole
  > SELECT * FROM ar_internal_metadata;
  key|value|created_at|updated_at
  environment|development|2017-09-11 23:14:10.815679|2017-09-11 23:14:10.815679
  ```

  After:
  ```
  $ RAILS_ENV=test rails dbconsole
  > SELECT * FROM ar_internal_metadata;
  key|value|created_at|updated_at
  environment|test|2017-09-11 23:14:10.815679|2017-09-11 23:14:10.815679
  ```

  Fixes #26731.

This test covers the case of 02da8aea.

Previously `exists?` was always eager-loading the includes values. But
now it is eager-loaded only when necessary since 07a611e0.

So the case of the eager-loading had not covered in the test.

We already found the longer sequence name, but we could not consider
whether it was the sequence name created by serial type due to missed a
max identifier length limitation. I've addressed the sequence name
consideration to respect the max identifier length.

Fixes #28332.

Currently `AUTO_INCREMENT` is implicitly used in the default primary key
definition. But `AUTO_INCREMENT` is not only used for single column
primary key, but also for composite primary key. In that case,
`auto_increment: true` should be dumped explicitly in the
`db/schema.rb`.

Fixes #30894.

This is the fix for the regression of #29848.

In #29848, I've kept existing select list in the subquery for the count
if ORDER BY is given. But it had accidentally affect to GROUP BY
queries also. It should keep the previous behavior in that case.

Fixes #30886.

For investigating the cause of failure.

https://travis-ci.org/rails/rails/jobs/287474883#L797-L799

Building association scope in join dependency should respect the parent
relation's aliases to avoid using the same alias name more than once.

Fixes #30681.

I don't think this is a good abstraction because the internal method is
used only if the relation need to be applied join dependency.

`relation.exists?` should reference correct aliases while joining tables
of has_many through associations.

s/Action Record/Active Record/

* When the adapter is missing, raise an exception that points out config
  typos and missing Gemfile entries. (We can assume that a non-builtin
  adapter was used since these are always available.)
* When loading an adapter raises a LoadError, prefix its error message
  to indicate that the adapter is likely missing an optional dependency.