Make the order of Hash#reverse_merge! consistent with HashWithIndifferentAccess

Enable `Layout/FirstParameterIndentation` cop

Set `RAILS_ENV` before load application file

We have some indentation cops. But now there is a little inconsistent
params indentations. Enable `Layout/FirstParameterIndentation` cop to
prevent newly inconsistent indentation added and auto-correct to
existing violations.

Since #29725, load application file when `dbconsole` command is executed.
However, if do not set `RAILS_ENV` before reading the application file,
can not connect to the env specified in option, so added the setting
of `RAILS_ENV`.

Use frozen string literal in activemodel/

Remove unused requires

Set `represent_boolean_as_integer` via `configuration`

Fix `create_with` with multiparameter attributes

Don't cache `scope_for_create`

Allow to pass a connection to the `dbconsole` command

[ci skip]

Replace Erubis with Erubi in a part of guide [ci skip]

Running the `console` and `dbconsole` commands with a regular argument
as the environment's name automatically expand it to match an existing
environment (e.g. dev for development).

This feature wasn't available using the `--environment` (a.k.a `-e`)
option.

People should rather rely on the `-e` or `--environment` options to
specify in which environment they want to work. This will allow us
to specify the connection to pick as a regular argument in the future.

Since 0a4f6009, it's possible to specify a 3-level database
configuration to gather connections by environment.

The `dbconsole` command will try to look for a database configuration
which points to the current environment but with such flavour, the
environment key is flushed out so let's add the ability to specify
the connection and pick `primary` by default to be consistent with
Active Record.

I investigated where `scope_for_create` is reused in tests with the
following code:

```diff
--- a/activerecord/lib/active_record/relation.rb
+++ b/activerecord/lib/active_record/relation.rb
@@ -590,6 +590,10 @@ def where_values_hash(relation_table_name = table_name)
     end

     def scope_for_create
+      if defined?(@scope_for_create) && @scope_for_create
+        puts caller
+        puts "defined"
+      end
       @scope_for_create ||= where_values_hash.merge!(create_with_value.stringify_keys)
     end
```

It was hit only `test_scope_for_create_is_cached`. This means that
`scope_for_create` will not be reused in normal use cases. So we can
remove caching `scope_for_create` to respect changing `where_clause` and
`create_with_value`.

Remove unused `@last`, `@order_clause`, and `@join_dependency`

Fix `create_with` using both string and symbol

Using `@last` and `@order_clause` was removed at 8bb52746 and 90d1524a.
`@join_dependency` was added at b9599502 but it is unused in the first
place.

This is related with #27680.

Since `where_values_hash` keys constructed by `where` are string, so we
need `stringify_keys` to `create_with_value` before merging it.

Because Arel is a private API and to describe `where_values_hash` keys
constructed by `where` are string.

Do not generate unused components contents in `app:update` task

Remove blank lines in setup

Currently, `app:update` generates all contents regardless of the
component using in application.

For example, even if not using Action Cable, `app:update` will generate
a contents related to Action Cable. This is a little inconvenient.
This PR checks the existence of the component and does not generate
unnecessary contents.
Can not check all options in this way. However, it will be able to
prevent the generation of unnecessary files.

Add a test case for overwriting existing condition on associations

Remove extra `.merge!(order: "id")` for `Relation#first` in tests

Fix boolean column migration script

Remove redundant instances of the word 'simply'

Remove redundant instances of the word 'simply' from documentation, on the basis that if it was simple, the user wouldn't be reading the docs