New codelab: colorist

[domesticmouse]

Pre-launch Checklist

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

If you need help, consider asking for advice on the #hackers-devrel channel on Discord.

[craiglabenz]

Feedback list while stepping through the codelab. (I will update this issue as I proceed.)

• It would be nice if the UP arrow cycled through past chat history. I realize this is not necessarily a quick feature to implement, so do with the thought what you will
  • Related: enabling text selection in the app would be nice. While I wait for VertexAI to turn on, I find myself wanting to copy-paste my previous prompt into the input to test it again.

[domesticmouse]

Feedback list while stepping through the codelab. (I will update this issue as I proceed.)

• It would be nice if the UP arrow cycled through past chat history. I realize this is not necessarily a quick feature to implement, so do with the thought what you will

  • Related: enabling text selection in the app would be nice. While I wait for VertexAI to turn on, I find myself wanting to copy-paste my previous prompt into the input to test it again.

I've implemented text selection in colorist_ui v0.0.4. I don't think I'm going to attempt to implement the up arrow functionality, that would require a fair bit more work to implement, and it doesn't really support what the app is about.

So, done?

[parlough]

I haven't reviewed the separate UI code or the codelab text, but what's in this PR looks good to me :)