Reject hexadecimal numbers with signs while validating numericality

Realign cache key diagram in method doc [ci skip]

Follow-up to #37669.

Add `config.active_storage.web_image_content_types` to allow applications
to add content types (like `image/webp`) in which variants can be processed,
instead of letting those images be converted to the fallback PNG format.

Update Gemfile.lock minimum Rack version to 2.0.9

Follow-up to #38991.

Add retry_jitter to 6.1 new framework defaults

Enable Rails/IndexBy and Rails/IndexWith cops

Update minimum Rack version to 2.0.9

Use __id__ to dedup records for transactional callbacks

Co-authored-by: NRyuta Kamizono <kamipo@gmail.com>

Preserve column comment on renaming column

Update activerecord changelog

Specify DB name in changelog and fix typo

This was added to the defaults for new applications in
e2cdffce, but we also need an entry in
the new framework defaults initializer for upgrading applications.

Followup to d3599d8a, which applied this
style to the existing codebase.

Since 28f81c05, if the `same_site:`
option is set to `:none` when creating a cookie, it will be passed
through to Rack. Support for `:none` was added in Rack 2.0.9, so we
should bump the minimum required version to ensure it's available.

While not a particularly good idea, it's possible to use `object_id` as
an attribute name, typically by defining a polymorphic association named
`object`. Since 718a32ca, transactional
callbacks deduplicate records by their `object_id`, but this causes
incorrect behaviour when the record has an attribute with that name.

Using `__id__` instead makes a naming collision much less likely.

Update scope documentation [ci skip]

Fix random CI fail due to cross-second time delay

Add missing backticks [ci skip]

* Bump rubocop to 0.82

The `Layout/Tab` cop has been renamed to `Layout/IndentationStyle`
ref: https://github.com/rubocop-hq/rubocop/releases/tag/v0.82.0

No other code changes required.

* Bump rubocop-rails to 2.5.2

No code-changes required.

[Tejas Bubane + Rafael Mendonça França]

Convert CoffeeScript to ES6 syntax

Follow up to 404e1a0a.

Don't gitignore tmp/pids/.keep

Since 04cfbc80, a keepfile is generated
in `tmp/pids/` to ensure that the directory always exists. However, the
gitignore pattern for `/tmp/*` meant it wasn't tracked in git.

To override that pattern we have to allow the `tmp/pids/` directory,
ignore everything inside it, then finally allow `tmp/pids/.keep` again.

Add `if_exists` option to `remove_index`

This PR allows for passing `if_exists` options to the `remove_index`
method so that we can ignore already removed indexes. This work follows
column `if/if_not_exists` from #38352 and `:if_not_exists` on `add_index`
from #38555.

We've found this useful at GitHub, there are migrations where we don't
want to raise if an index was already removed. This will allow us to
remove a monkey patch on `remove_index`.

I considered raising after the `index_name_for_remove` method is called
but that method will raise if the index doesn't exist before we get to
execute. I have a commit that refactors this but after much
consideration this change is cleaner and more straightforward than other
ways of implementing this.

This change also adds a little extra validation to the `add_index` test.
Fix `nodoc` on edited methods.

Fix unscoping association scope on joins not to raise an error

active_record_validations.md grammer fix [ci skip]

An extremely small readability change to line 269 [ci skip].

#29589 changed merging scope order to allow to unscope default scopes on
association scope (#29611), but that caused a regression #38811 that
accidentally allow join constraint which is required.

```
% bin/test test/cases/associations/has_many_associations_test.rb -n test_unscopes_the_default_scope_of_associated_model_when_used_with_include
Run options: -n test_unscopes_the_default_scope_of_associated_model_when_used_with_include --seed 32978

# Running:

E

Error:
HasManyAssociationsTest#test_unscopes_the_default_scope_of_associated_model_when_used_with_include:
NoMethodError: undefined method `children' for nil:NilClass
    ~/rails/activerecord/lib/active_record/associations/join_dependency/join_association.rb:39:in `block in join_constraints'
    ~/rails/activerecord/lib/active_record/associations/join_dependency/join_association.rb:30:in `reverse_each'
    ~/rails/activerecord/lib/active_record/associations/join_dependency/join_association.rb:30:in `with_index'
    ~/rails/activerecord/lib/active_record/associations/join_dependency/join_association.rb:30:in `join_constraints'
    ~/rails/activerecord/lib/active_record/associations/join_dependency.rb:171:in `make_constraints'
    ~/rails/activerecord/lib/active_record/associations/join_dependency.rb:196:in `block in walk'
    ~/rails/activerecord/lib/active_record/associations/join_dependency.rb:196:in `each'
    ~/rails/activerecord/lib/active_record/associations/join_dependency.rb:196:in `flat_map'
    ~/rails/activerecord/lib/active_record/associations/join_dependency.rb:196:in `walk'
    ~/rails/activerecord/lib/active_record/associations/join_dependency.rb:90:in `block in join_constraints'
    ~/rails/activerecord/lib/active_record/associations/join_dependency.rb:87:in `each'
    ~/rails/activerecord/lib/active_record/associations/join_dependency.rb:87:in `flat_map'
    ~/rails/activerecord/lib/active_record/associations/join_dependency.rb:87:in `join_constraints'
    ~/rails/activerecord/lib/active_record/relation/query_methods.rb:1226:in `build_join_query'
    ~/rails/activerecord/lib/active_record/relation/query_methods.rb:1211:in `build_joins'
    ~/rails/activerecord/lib/active_record/relation/query_methods.rb:1091:in `build_arel'
    ~/rails/activerecord/lib/active_record/relation/query_methods.rb:1063:in `arel'
    ~/rails/activerecord/lib/active_record/relation/finder_methods.rb:419:in `block in limited_ids_for'
    ~/rails/activerecord/lib/active_record/relation.rb:867:in `skip_query_cache_if_necessary'
    ~/rails/activerecord/lib/active_record/relation/finder_methods.rb:419:in `limited_ids_for'
    ~/rails/activerecord/lib/active_record/relation/finder_methods.rb:398:in `apply_join_dependency'
    ~/rails/activerecord/lib/active_record/relation.rb:839:in `block in exec_queries'
    ~/rails/activerecord/lib/active_record/relation.rb:867:in `skip_query_cache_if_necessary'
    ~/rails/activerecord/lib/active_record/relation.rb:834:in `exec_queries'
    ~/rails/activerecord/lib/active_record/relation.rb:639:in `load'
    ~/rails/activerecord/lib/active_record/relation.rb:250:in `records'
    ~/rails/activerecord/lib/active_record/relation/finder_methods.rb:508:in `find_take'
    ~/rails/activerecord/lib/active_record/relation/finder_methods.rb:98:in `take'
    ~/rails/activerecord/lib/active_record/relation/finder_methods.rb:458:in `find_one'
    ~/rails/activerecord/lib/active_record/relation/finder_methods.rb:442:in `find_with_ids'
    ~/rails/activerecord/lib/active_record/relation/finder_methods.rb:69:in `find'
    ~/rails/activerecord/test/cases/associations/has_many_associations_test.rb:2689:in `block in <class:HasManyAssociationsTest>'

bin/test test/cases/associations/has_many_associations_test.rb:2683
```

Required join constraint should not be allowed to unscoping.

Fixes #38811.

Remove unused Arel visitors in the code base

This removes ibm_db, informix, mssql, oracle, and oracle12 Arel visitors
which are not used in the code base.

Actually oracle and oracle12 visitors are used at oracle-enhanced
adapter, but now I think that those visitors should be in the adapter's
repo like sqlserver adapter and the dedicated Arel visitor
(https://github.com/rails-sqlserver/activerecord-sqlserver-adapter/blob/master/lib/arel/visitors/sqlserver.rb),
otherwise it is hard to find a bug and review PRs for the oracle
visitors (e.g. #35838, #37646), since we don't have knowledge and
environment enough for Oracle.