Remove 'if exists' from drop table statement then use `table_exists?`

Since 'drop table if exists' statement does not always work with
some databases such as Oracle.

Is this a thing we want?

Note current duplication between the `assert_select` section here, and
the corresponding release note entry... does this detail *move* from
there to here?

[ci skip]

Refactor add_constraints complex loop conditional

Shorten ActionView::Base doc summary line. [ci skip]

Clarify Rails uses erubis not stdlin ERB. [ci skip]

Remove '*' which doesn't belong [ci skip]

I found an * does not work in Markdown notation. It should be removed.

Add and Remove string/strip require

Method .strip_heredoc is defined in
active_support/core_ext/string/strip.rb so we need to require it.

[fixes #16677]

[ActiveJob] TestCase

We're seeing too many failures to believe otherwise.

This reverts commits bc116a55,
cbde413d,
bf0a6793, and
2440933f.

ActiveJob: Implemented enqueue_at for QueueClassic

[ci skip] Fix a typo in the doc of MessageDelivery

Do not swallow exception on NameError within constant.

Now we keep only the common code and move the specific code to the gems

This breaks the two branches of the `if reflection.last` and `else`
to clearer see where the two methods can be refactored. Eventually
we hope to remove the need for these separated methods altogether.

Move the first branch outside the loop

This code doesn't need to be in the loop because it it always affects
the last chain. `get_bind_values` and `add_constraints` must match
in this context because `get_bind_values` is the caching of `add_constraints`

Use each_cons to remove need for `chain[i + 1]`

The `chain[i + 1]` is confusing because it's not immediately obvious
what it's trying to achieve. The use of `each_cons` makes it clear
we need to get the `next_reflection`.

Fixes https://github.com/rails/rails/issues/9933.

use self instead of #read_attribute

Fix for configuring rails guide [ci skip]

`ActiveSupport::Logger` has no concept like auto flushing since it has no userspace buffering.
It's a remnant of `ActiveSupport::BufferedLogger` epoch which was since removed from rails.

Allow polymorphic routes with nil when a route can still be drawn

Clarify that /console is an optional feature

(/console is not mounted by default with web-console 2.0.)