Allow authentication header to not have to specify 'token=' key.

Fixes: https://github.com/rails/rails/issues/17108.
Correct test description for large integer test
[Testing guide] Use "Fixtures API" instead of "fixture api".
[Testing guide] Using "Fixtures API" consistently

- In guides, "API" is used consistently instead of "api".
- Reason behind replacing "fixtures API" to "Fixtures API" is because
  here we are referring to the concept of "fixtures". In other places in
  the guide "fixture" OR "fixtures" is referred to the single or
  multiple instances of test data.
- This is also followup of https://github.com/rails/docrails/commit/aa9d1332b20305dd860b21a7ada06c5252bebad5#commitcomment-8497376.
Explain that default_scope also influences update_all

This was not explicitly stated before and I needed to try it out to be
certain. A little explicit statement in the API docs might help here.
Fixing documentation in JSON#from_json

Commit d67b289 introduced a tiny regression in the docs for #from_json,
true needs to be included when the root node is present.
Remove is_a? check when ignoring tables

Technically changes the API, as it will allow any object which responds
to `===`. Personally, I think this is more flexible.
Fix includes on association with a scope containing joins along with conditions
on the joined assoiciation
Creates an ApplicationMailer and layout by default, including html and body tags to reduce spam score
Move test that depends on ActiveRecord

This commit moves a test from `test/template` to `test/activerecord` since the
test depends on ActiveRecord.

This matches the documentation from [RUNNING_UNIT_TESTS](https://github.com/rails/rails/blob/f28d1ddd507174ac233b773cc4f35c3c05ad32e7/actionview/RUNNING_UNIT_TESTS.rdoc):

> Test cases in the test/activerecord/ directory depend on having activerecord and sqlite3 installed.
> If Active Record is not in actionview/../activerecord directory, or the sqlite3 rubygem is not installed, these tests are skipped.
> Other tests are runnable from a fresh copy of actionview without any configuration.

---

More details about this commit.

All the tests starting with `require 'active_record_unit'` are already
inside `test/activerecord`, except for the one test this commit moves.

If you don't have `active_record` on your machine, the following command
currently fails on master:

```bash
```
[ci skip] Fix class name of middleware.
Specified beta branch for web-console gem
Test using `ActionController::TestCase` with engines

Reference #17453

[Godfrey Chan, Washington Luiz]
Correct example in the engines testing guide [ci skip]

Reference #17453
Fix cases where the wrong name is passed to `Formatter#generate`

These are currently working "by accident" because `match_route` does not check
that the name is valid.
Deprecate passing an invalid name to `Formatter#generate`

The internal tests that (incorrectly) relied on this were already fixed in
938d130. However, we cannot simply fix this bug because the guides prior to
b7b9e92 recommended a workaround that relies on this buggy behavior.

Reference #17453
Deprecate `use_route` in controller tests

Reference #17453
Don't show the warning if we're already raising the error anyway

If the route set is empty, or if none of the routes matches with a score > 0,
there is no point showing the deprecation message because we are already be
raising the `ActionController::UrlGenerationError` mentioned in the warning.

In this case it is the expected behavior and the user wouldn't have to take any
actions.
Adding simple docs for ActionDispatch::Flash::FlashHash#to_session_value
adding nodoc to private methods