[forge2d codelab] Use flame_kenney_xml instead of manual XML parsing

[spydon]

This simplifies the forge2d codelab by using the flame_kenney_xml package (official Flame package) for parsing the Kenney sprite sheets. (It pretty much contains the same code as @domesticmouse previously wrote for this codelab)

Pre-launch Checklist

• [x] I read the Effective Dart: Style recently, and have followed its advice.
• [x] I signed the CLA.
• [x] I updated/added relevant documentation (doc comments with ///).
• [x] All existing and new tests are passing.

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[spydon]

Oh, it bumped some dependencies when running codelab_rebuild too.

[spydon]

The diffs are not correct, I should have just edited the files and getting the diffs instead of directly editing the code_rebuild.yaml :sweat_smile:

[domesticmouse]

Thank you for this PR @spydon!

I doubt I'm going to have time to update the codelab text and domesticmouse/forge2d_workshop_presentation before I/O Connect Bengaluru. See how the next couple of weeks go.

[spydon]

Thank you for this PR @spydon!

I doubt I'm going to have time to update the codelab text and domesticmouse/forge2d_workshop_presentation before I/O Connect Bengaluru. See how the next couple of weeks go.

Thanks a lot for fixing it up! I was a bit too busy now with I/O Connect Berlin and FlutterCon.

I might be able to help with the text once I'm back from Berlin. :)

[domesticmouse]

I think I've updated the codelab text. Just waiting on @RedBrogdon to sign off the updated codelab for publication before landing this PR.