Fix generator command for nested (namespaced) rails engine (take 2)

Remove unused DdlHelper in ForeignKeyTest

Use ActiveRecord `bigint` type, not SQL literal bigint

Oracle database itself does not have `bigint` SQL type, then it gets `ORA-00902: invalid datatype`.

It can be addressed by using ActiveRecord `bigint` type
because Oracle enhanced adapter recognizes ActiveRecord `bigint` type
and transfer it to its equivalent SQL type `NUMBER(19)`.

Should keep the primary key column order

Fixes CI failure caused by #27961.

https://travis-ci.org/rails/rails/jobs/201472146#L2390-L2409

Not ants were harmed! 🐜 [ci skip]

Simplify and optimize Postgres query for primary_keys()

Fix the return of `deprecate_methods` in doc [ci skip]

Freeze fragment cache related instrument name.

primary_keys(table) needs to query various metadata tables in Postgres
to determine the primary key for the table. Previously, it did so using
a complex common table expression against pg_constraint and
pg_attribute.

This patch simplifies the query by using information_schema tables.
This simplifies the logic, making the query far easier to understand,
and additionally avoids an expensive unnest, window function query, and
common table expression.

Add `default_index_type?` to the generic schema dumper doesn't have the knowledge about an index type

Add `default_index_type?` to the generic schema dumper doesn't have the knowledge about an index type

Fix `remove_index` to be able to remove expression indexes

Omit redundant `using: :btree` for schema dumping

Refactor `test_find_by_does_not_use_statement_cache_if_table_name_is_changed`

Fix unscope with subquery

The `default` arg of `index_name_exists?` makes to optional

Extract `quoted_binary` and use it rather than override `_quote`

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 #27980

Closes #27979

`supports_primary_key?` was added to determine if `primary_key` is
implemented in the adapter in f0602214. But we already use `primary_key`
without `supports_primary_key?` (207f266c, 5f3cf424) and using
`supports_primary_key?` has been removed in #1318. This means that
`supports_primary_key?` is no longer used in the internal and Active
Record doesn't work without `primary_key` is implemented (all adapters
must implement `primary_key`).

Closes #27977

These files are not using `strip_heredoc`.

Closes #27976

Removed the `attribute_accessors` required file:

So queries are not run against the previous table name.

Closes #27953

Also not needed on this file, call to `mattr_accessor` got removed in https://github.com/rails/rails/commit/9e98f3f7e61dfce0a48948c8d296400af8bfaf21#diff-1ecd313ff0ab827af30014553cf8918dL76

- This file is no more needed, the call to `cattr_reader` were removed in https://github.com/rails/rails/commit/9e2948e750fa3f641f20adad4b4ecae89b35faa7#diff-c5146df11f35304765e9ceebed108f57L60 and https://github.com/rails/rails/commit/1fe0a1b5ebebb1372968606b85ce08b93bc145c8#diff-c5146df11f35304765e9ceebed108f57L99

Add Time#blank? to blank_test

Add `Style/EmptyLinesAroundMethodBody` in `.rubocop.yml` and remove extra empty lines