onroad/alerts: replace magic numbers with named constants

[deanlee]

The alert_heights map was also removed because it didn't adapt to changes in window height, causing resizing issues. It was also non-constant, which was not ideal.

[github-actions]

Thanks for contributing to openpilot! In order for us to review your PR as quickly as possible, check the following:

• Convert your PR to a draft unless it's ready to review
• Read the contributing docs
• Before marking as "ready for review", ensure:
  • the goal is clearly stated in the description
  • all the tests are passing
  • the change is something we merge
  • include a route or your device' dongle ID if relevant

[github-actions]

UI Screenshots

[adeebshihadeh]

Can you add one of each alert to the UI report?

We'll be touching this code a lot more soon, and it would be nice if the UI report showed the changes.

[deanlee]

#33394

done, but not sure why the ui report is still displaying the old information.could it be that the updated results only appear after merging?

[maxime-desroches]

@deanlee Yes, the ui_preview.yaml workflow is always taken from master since it has access to some Github Secrets.
The best way to test your new ui preview is to merge the new ui_preview.yaml in the master branch of your fork and then to do a PR againt the master branch of your fork.

[adeebshihadeh]

I don't actually think this is better. The locality of all these numbers makes the paintEvent readable. If anything's duplicated, let's pull it into a constant, but otherwise I think this is fine.