Modernize tutorials

At long last, the Tutorial catches up with the current release.

- Big picture discussion of our navigation story (see the end of Tutorial2.md)

- Use `AndroidScreen` and drop `ViewRegistry`

- Better, more consistent use of `BackStackScreen`

- Use `View.setBackHandler`

- Use `TextController`

- Use `RequestContext.eventHandler`

- Delete a lot of `// Exactly what the function name and the code say` comments

- Hint at the existance of `ComposeWorkflow` and `Overlay` without turning this into a complete rewrite

- More consistent naming, code style for actions and event handlers in `Screen` renderings
  - Event handler fields are named `onVerbPhrase`, like `onBackPressed`
  - Action names are verb phrases describing the action that is being taken, not the event that is being handled
  - Output names are generally in terms of the semantic event being reported to the parent, rather than describing what the parent will do

Thus:

```kotlin
return TodoListScreen(
  onRowPressed = { context.actionSink.send(reportSelection(it)) }
```

```kotlin
  private fun reportSelection(index: Int) = action {
    // Tell our parent that a todo item was selected.
    setOutput(TodoSelected(index))
  }
```

(Although most of these are inlined as `eventHandler("…") {}` calls.)

I've mainly focussed on updating what exists, not extending its coverage further. Once this is merged I'd like to follow up and do more:

- Introduce `Overlay` properly
  - How about move `TodoEditScreen` to a `BottomSheetDialog`?
  - Could be too noisy, `BottomSheetDialog` is a bastard.
  - If that's the case create a separate sample for it.
- Introduce `Compose`.
  - I think the way to go is add a sixth step that updates `TodoListScreen`, talk about getting rid of that `RecyclerView`.
  - Could point out that the existing workflows and tests are unchangedn

Author: rjrjr

samples/tutorial/README.md

@@ -1,29 +1,9 @@
 # Tutorial
 
-## Stale Docs Warning
-
-**This tutorial is tied to an older version of Workflow, and relies on API that has been deprecated or deleted.**
-The general concepts are the same, and refactoring to the current API is straightforward,
-so it is still worthwhile to work through the tutorial in its current state until we find time to update it.
-(Track that work [here](https://github.com/square/workflow-kotlin/issues/905)
-and [here](https://github.com/square/workflow-kotlin/issues/884).)
-
-Here's a summary of what has changed, and what replaces what:
-
-- Use of `ViewRegistry` is now optional, and rare.
-  Have your renderings implement `AndroidScreen` or `ComposeScreen` to avoid it.
-- The API for binding a rendering to UI code has changed as follows, and can all
-  be avoided if you use `ComposeScreen`:
-   - `ViewFactory<in RenderingT : Any>` is replaced by `ScreenViewFactory<in ScreenT : Screen>`.
-   -`LayoutRunner<RenderingT : Any>` is replaced by `ScreenViewRunner<in ScreenT : Screen>`.
-   - `LayoutRunner.bind` is replaced by `ScreenViewFactory.fromViewBinding`.
-- `BackStackScreen` has been moved to package `com.squareup.workflow1.ui.navigation`.
-- `EditText.updateText` and `EditText.setTextChangedListener` are replaced by `TextController`
-
 ## Overview
 
 Oh hi! Looks like you want build some software with Workflows! It's a bit different from traditional
-Android development, so let's go through building a simple little TODO app to get the basics down.
+Android development, so let's go through building a simple little To-Do app to get the basics down.
 
 ## Layout
 
@@ -33,7 +13,7 @@ To help with the setup, we have created a few helper modules:
 
 - `tutorial-views`: A set of 3 views for the 3 screens we will be building, `Welcome`, `TodoList`,
   and `TodoEdit`.
-- `tutorial-base`: This is the starting point to build out the tutorial. It contains layouts that host the views from `TutorialViews` to see how they display.
+- `tutorial-base`: This is the starting point to build out the tutorial.
 - `tutorial-final`: This is an example of the completed tutorial - could be used as a reference if
   you get stuck.