Remove multi-file DartPad usages from cheatsheet

[MaryaBelanger]

Part of #5382

• The tests feature contained main for each example, but that features being removed. The examples need main to run, and also are not helpful without the feedback that the tests provided, so we're adding the tests to code visible in each dartpad.

  • Comment at the top of each that this part is tests, don't edit
  • Will have to adjust the tests for more useful messages to users.
  • Since main is a big focus now, add a new section on the main function at the top of the cheatsheet.

• Also remove hint and solution feature and place in expandable "solution" section under each example.

• Rewrite the intro section to explain the new way the page works.

[github-actions]

Visit the preview URL for this PR (updated for commit 449e0c5):

https://dart-dev--pr5392-cheatsheet-crrjrj27.web.app

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[parlough]

Thanks for raising your concerns. I think we can still figure out something useful here.

Do you have time to meet for 30 minutes today (12/5)? Might be easier to discuss our options synchronously.

[MaryaBelanger]

@parlough I was already planning to leave the new section on main for another PR, just to get this one finished. But then I saw in the intro that it says:

The Dart language is designed to be easy to learn for coders coming from other languages, but it has a few unique features. This codelab walks you through the most important of these language features.

In that light, going over main doesn't really fit to the theme of the page. What do you think?

[parlough]

I think it's fine to move to a follow-up CL, but I'd say it does fit the theme of being a unique (and cool) feature to Dart. Python and JS don't have a main method, Java (until a few weeks ago) required a complicated static public void main(String[] args) in a class, and C# requires something similar.

I'd also be happy to write it out if you think it's valuable. Just let me know!

[MaryaBelanger]

Oh perfect, didn't know that and that info will help me write the section too. Created #5414 , thanks!

I'd also be happy to write it out if you think it's valuable. Just let me know!

If you'd prefer getting it into this PR, then by all means feel free to add it! But otherwise I'm happy to handle it too!

[parlough]

This is great @MaryaBelanger!! Thanks so much for taking this on, especially unplanned and on a short notice.

I was worried how it would turn out without all of the original DartPad functionality, but it's not too different and I think the core benefits of the page still remain.

I left a few suggestions and questions, but nothing blocking.

A few sample tests do need still need to be updated to move away from _result, but I'd be happy to do that (and any of the other comments) as follow-up if you have other things you have to/prefer to work on right now. Just let me know :)

[MaryaBelanger]

@parlough Thanks for the thorough review. I went through and there were a lot of _results still in use so I got rid of all of them. I also changed any "try" language in the solution/hint text to "use" like you suggested in a few places (there were a few more).

Edit: idk why the builds failing I updated docker in this PR... is that ok or should it be another PR?

[parlough]

Thank you so much, looks great!