Initial attempt at combining tutorials and codelabs

[mit-mit]

Issues with the current design:

• There is no functional difference between tutorials and codelabs; for the purposes of our docs there's no reason to distinguish them (I'll be using "tutorials" referring to both, as the docs should)
• The positioning of "Tutorials & Codelabs" right at the top of the sidenav is misrepresentative - it implies that's a good place for users to start exploring the docs.
• A aggregate "tutorials" page should have them listed in some sort of logical progression of skill building, and that progression should be complete. Not the case here.

After some discussion, here's how we've decided to progress with solving this:

1. Add a preliminary "Getting Started" page to the top of the sidenav

   • Single page, summarizes key areas of the docs site and how to progress through them, why you might need each one. Could include pointers to tutorials, as well as language tour pages, anything.
   • Focus on Language, Libraries, and the Command-line app tutorial
   • I'm thinking the page should have a very light narrative calling out the highlights of each topic-area the docs cover, in the order that makes sense for the typical new user's goals. Rough example, but something like:
     • "To start using Dart, familiarize yourself with some of the syntax on these pages (link(s) to some of the better introductory examples we have, the command-line app tutorial for a more in-depth intro, etc.)....."
     • "Dart is an object oriented language, so make sure to read about classes and their behaviors over here..... "
     • "To build real programs, you'll need to understand Dart's core libraries and what they offer, so skim through this to get a an idea....(library tour, whatever)..... "
     • "The Dart ecosystem uses packages to manage shared software, so next you should learn how to effectively manage your own software as packages, as well as how to utilize our rich package library over here....."
     • "Dart is meant to be a powerful solution to developing multiplatform apps. Learn about development tools and tips for Dart over here best development section basics page..... "

2. Remove the "Tutorials & Codelabs" section from the side nav

   • Re-position the tutorials listed on those pages alongside their overarching topic pages
   • E.g., How the "Write command line apps" and "Write HTTP servers" tutorials are listed under "Development" > "Command line & server apps" already
   • (@parlough is this essentially how the Flutter IA restructure is working out? Any advice before we get started?)

3. Change all mentions of "codelab" to "tutorial" across the site

[atsansone]

@mit-mit : Love this suggestion. I added a few notes.

[atsansone]

issue: Need to add commas to the dependent clauses.

Suggested change

	If you like learning via coding exercises
	checkout the [Dart koans](/codelabs/dart-cheatsheet).
	For a more textual introduction see the
	[language intro](/language).
	The Language menu on the left also has tutorials
	on more detailed topics, and tutorials written
	for those with existing knowledge of other programming languages.
	If you like learning via coding exercises,
	check out the [Dart koans](/codelabs/dart-cheatsheet).
	To get an in-depth explanation, see the
	[language intro](/language).
	The Language menu also includes tutorials on more
	detailed topics and for those with existing knowledge
	of other programming languages.

[atsansone]

issue: We don't need to describe the TOC. We can link to it.

Suggested change

	The Libraries menu contains tutorials on the Dart core libraries,
	including collections, math, asynchronous programming, and I/O.
	Libraries contains tutorials on the Dart core libraries,
	including collections, math, asynchronous programming, and I/O.

[atsansone]

suggestion: Write as shorter sentences per GSG.

Suggested change

	This tutorial teaches you about Dart’s [null-safe type system](/null-safety),
	which was introduced in Dart 2.12. When you opt into null safety,
	types in your code are non-nullable by default,
	meaning that values can’t be `null` unless you say they can be.
	This tutorial explains Dart’s [null-safe type system](/null-safety).
	Dart 2.12 introduced null safety and Dart 3 made it the default setting.
	With null safety, types in your code default to non-nullable.
	This means that values can’t be `null` unless you say they can be.

[atsansone]

suggestion: Add a link to DartPad.

Suggested change

	This page uses embedded DartPads to display exercises.
	This page uses embedded [DartPads](/tools/dartpad) to display exercises.

[atsansone]

suggestion: Phrase as a call to action and avoid "here".

Suggested change

	Congratulations, you've finished the tutorial! If you'd like to learn more, here
	are some suggestions for where to go next:
	Congratulations, you've finished the tutorial!
	To learn more about null safety, we suggest the following topics:

[atsansone]

question: This page isn't about DartPad, so I would delete that reference. Also, I don't recommend linking to the issue. The page has a button that can be clicked to review the code, then create an issue or PR.