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

Suppose you have two resources routed in the following manner:

```ruby
resources :blogs do
  resources :posts
end

resources :posts
```

When using polymorphic resource routing like `url_for([@blog, @post])`, and `@blog` is `nil` Rails should still try to match the route to the top-level posts resource.

Fixes #16754
Since /console is an optional feature, mention <%= console %> instead.

(/console is not mounted by default with web-console 2.0.)
Merge pull request #16747 from rsutphin/web-console-gemfile-comment

Clarify that /console is an optional feature
Keep it closer to the original wording [ci skip]
Merge pull request #16755 from codeodor/master

Allow polymorphic routes with nil when a route can still be drawn
Clear schema cache before each test
Fix for configuring rails guide

`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.
Merge pull request #16763 from brainopia/patch-1

Fix for configuring rails guide [ci skip]
Clear schema cache before each test
Time#change throws exception with an out-of-range :usec

https://github.com/rails/rails/commit/98b46bf5e201307cae56ee14bf41363a539779c5
did not properly handled out-of-range `:usec`s.

Passing a `:usec` that's out of range now throws an `ArgumentError` as it
should.

Fixes #16759.
Time#change supports a :nsec option.

If used together with a :usec option, both values will be summed.

Closes #16392.