Closes #16907.

[Matthew Draper & Yves Senn]

[guides] 4.2 release notes: added technical details for Adequate Record

Improve environment config templates consistency

* Fix long lines;
* Use simple quotes for string literals when interpolation is not used.

Explain ERB space removal.

[ci skip]

Use dynamic path for dummy app location in plugin's test_helper.rb

[ci skip]

[ci skip] Fix typo `equals to` --> `equal to`

Ruby 2.2 knows this, and no longer matches it with [[:space:]], so it's
not a good candidate for testing String#squish.

add implementation of respond_to? for ActiveSupport::Duration

Add test jobs task

This is much less common than string literal appends, so add a special
case method for it.  Maybe fixes bug reported by @jeremy on 97ef6361

simplify test_adapter

Singular credit_card controller name changed to plural [ci skip]

* Disallow deserialization of non-primitive objects
* Broaden coverage; remove superfluous tests

ERB compiler guarantees safe_append= will be called with a string, so
nil checks don't make sense.  Anything else calling this method should
check for nil themselves before calling

Rescue `Rack::Utils::ParameterTypeError` instead of `TypeError`

Add support for `:nsec` option to `Time#change`

As of rack/rack@167b6480235ff00ed5f355698bf00ec2f250f72e, Rack raises
Rack::Utils::ParameterTypeError which inherits TypeError.

In terms of the behavior, Rescuing TypeError still works but this
method shouldn't rescue if TypeError is raised for other reasons.

Closes #16392.

use `allow_blank` option instead of custom condition

Data corruption risk: Roll back open transactions when the running thread is killed.

This reverts commit 21ec7fef.

Per #16911, there's actually a good reason for a "blank" value to have a
useful `to_s` here. So let's also add some tests to prove that.

Change ActiveJob test directory to "test/jobs" [ci skip]

Improved the error messaging for the DangerousAttributeError exception