Why:

* When getting an error that generates a screenshot it would be helpful
  to be able to ctrl+click it to quickly open it in the browser, which
  does not work with relative paths

This change addresses the need by:

* Changing `image_path` to disregard the relative path and use the
  absolute one instead

Not everyone uses iTerm2 and whereas Terminal.app on a mac just ignores
that and outputs the path, other terminals like those on Ubuntu do not.
A friendlier default is one that works by default.

Closes #31159
Closes #30957

In Rails engine `Rails.root `returns the path of the dummy application.
Therefore, there is no `tmp` directly where the test is running, so can
not get the screenshot.
For this reason, instead of directly specifying tmp, retrive screenshot by
relative path from the current directory.

Fixes #30405

Without this, `display_image` raises an error as follwing:

```
RuntimeError: can't modify frozen String
    rails/actionpack/lib/action_dispatch/system_testing/test_helpers/screenshot_helper.rb:72:in `display_image'
    rails/actionpack/test/dispatch/system_testing/screenshot_helper_test.rb:40:in `block (2 levels) in <class:ScreenshotHelperTest>'
```

This reverts commit 3420a145, reversing
changes made to afb66a5a.

3 output types are supported:
- simple: only display the screenshot path
- artifact: display the screenshot in the terminal, using the artifact protocol (supported by some CI)
- inline (default): display the screenshot in the terminal, inline (supported by some terminals)

You can force the output type by setting the `RAILS_SYSTEM_TESTING_SCREENSHOT` environment variable

Previously the system test subclasses would call `driven_by` when the
app booted and not again when the test was initialized which resulted in
the driver from whichever class was called last to be used in tests.

In rails/rails#28144 the `driven_by` method was changed to run `use` on
setup and `reset` on teardown. While this was a viable fix this really
pointed to the problem that system test `driven_by` was a global
setting, rather than a per-class setting.

To alieviate this problem calling the driver should be done on an
instance level, rather than on the global level. I added an `initialize`
method to `SystemTestCase` which will call `use` on the superclass
driver. Running the server has been moved to `start_application` so that
it only needs to be called once on boot and no options from `driven_by`
were being passed to it.

This required a largish rewrite of the tests. Each test needs to utilize
the subclass so that it can properly test the drivers.
`ActionDispatch::SystemTestCase` shouldn't be called directly anymore.

`Capybara::RackTest::Driver` does not support taking screenshots. If call
`#save_screenshot` on `Capybara::RackTest::Driver` will raise the error.

```ruby
Error:
UsersTest#test_visiting_the_index:
Capybara::NotSupportedByDriverError: Capybara::Driver::Base#save_screenshot
```

To prevent errors, if driver does not support screenshot, do not call it.

This renames the system test helper file to be application system test
case to match what the rest of Rails does. In the future we should
consider changing the test_helper to match.

We only want the file name to include the word `failures` if it failed,
not any time the user wants to take a screenshot during a test run.

* Move system tests back into Action Pack
* Rename `ActionSystemTest` to `ActionDispatch::SystemTestCase`
* Remove private base module and only make file for public
`SystemTestCase` class, name private module `SystemTesting`
* Rename `ActionSystemTestCase` to `ApplicationSystemTestCase`
* Update corresponding documentation and guides
* Delete old `ActionSystemTest` files