avoid using alias in generators

Ruby's alias produces public methods, causing a spurious Thor task
to be created.  For example, this is the reason MigrationGenerator
currently has two tasks:

    > ActiveRecord::Generators::MigrationGenerator.all_tasks.keys
    => ["singular_name", "create_migration_file"]

singular_name was meant to be an attribute, not a task.  Because it's
public, it gets called as a task every time the generator is invoked.

The fix is to ensure all generator methods have the correct
visibility.
Fix migrations with enable_extension

When using ActiveRecord::Base.table_name_prefix and/or
table_name_suffix, extension names got the same treatment as table names
when running migrations. This led to migrations that tried to call, for
example, enable_extension("prefix_hstore") on the connection.
Hash#deep_*_keys(!) recurse into nested arrays.

Following methods now recursively transform nested arrays, too.

* Hash#deep_transform_keys
* Hash#deep_transform_keys!
* Hash#deep_stringify_keys
* Hash#deep_stringify_keys!
* Hash#deep_symbolize_keys
* Hash#deep_symbolize_keys!
Check authentication scheme in Basic auth

`authenticate_with_http_basic` and its families should check the authentication
schema is "Basic".

Different schema, such as OAuth2 Bearer should be rejected by basic auth, but
it was passing as the test shows.

This fixes #10257.
Run login_procedure only when the auth_scheme is valid
Fix serialized field returning serialized data after update_column
Fixes Issue #13466.

Changed the call to a scope block to be evaluated with instance_eval.
The result is that ScopeRegistry can use the actual class instead of base_class when
caching scopes so queries made by classes with a common ancestor won't leak scopes.
Fixed a problem where `sum`, `size`, `average`, `minimum` and `maximum` used
with a grouping was not returning a Hash.
Reorganize ActiveRecord tasks [Arun Agrawal & Abd ar-Rahman Hamidi]
Put attr_reader in with all of the other instance methods

This makes the grouping make a little more sense
Use destructured arguments when looping through pairs

Minor refactoring of looping behavior for aggregation
Default config.assets.digests to true in development
Make `:index` in migrations work with all column types
early return on delete and destroy methods

When delete or destroy is called on all records nothing
is deleted or destroyed. Intead of running through the code and still
not deleteing anything, we should early return
pg guide, move introductory sentences into main content. [ci skip]

This is a reaction to https://github.com/rails/rails/commit/7ca75f3789e316b6f3dc1f8000ec4f85c8ba32ea#commitcomment-6303828
Merge pull request #14962 from arunagw/aa-fix-rake-activerecord

Reorganize ActiveRecord tasks [Arun Agrawal & Abd ar-Rahman Hamidi]
pg, add missing nodocs for extracted modules.
pg, re-introduce `PostgreSQL::Utils` to unify schema/table extraction.

Partial revert of c0bfc3f412834ffe8327a15ae3a46602cc28e425
Merge pull request #15160 from sgrif/sg-destructured-each

Use destructured arguments when looping through pairs
Merge pull request #14126 from schuetzm/index_option_for_column

Make `:index` in migrations work with all column types