When a host is not specified for an `ActionController::Renderer`'s env,
the host and related options will now be derived from the routes'
`default_url_options` and `ActionDispatch::Http::URL.secure_protocol`.

For example, with:

  ```ruby
  Rails.application.default_url_options = { host: "rubyonrails.org" }
  Rails.application.config.force_ssl = true
  ```

Before:

  ```ruby
  ApplicationController.renderer.render inline: "<%= blog_url %>"
  # => "http://example.org/blog"
  ```

After:

  ```ruby
  ApplicationController.renderer.render inline: "<%= blog_url %>"
  # => "https://rubyonrails.org/blog"
  ```

As a consequence, Action Text attachment URLs rendered in a background
job (a la Turbo Streams) will now use `Rails.application.default_url_options`.

Fixes #41795.
Fixes hotwired/turbo-rails#54.
Fixes hotwired/turbo-rails#155.