convert the implementation of the action to Dart

[devoncarew]

Convert the implementation of the action to Dart:

• a mostly direct translation from the Bash implementation to Dart
• kept the dart.yml CI the same, so we could verify correct behavior of the port
• as part of the port, addressed an issue related to auto-detection of the platform architecture (fix Automatically choose the correct architecture #59)
• also, added a new action output - dart-version
• done as part of general updates to the setup action #62
• updated the changelog w/ the relevant changes, and rev'd the action version to 1.5.0-dev
• updated with our std CONTRIBUTING.md file from dart-lang/.github
• added a DEVELOPING.md file, with some info about how the action is built and how to work on it

[devoncarew]

@joshualitt + @srujzs - can you review the js interop code (lib/node/*), the bootstrap script (lib/main.mjs), and anything else that looks interesting? Thanks!

[joshualitt]

The JS interop code looks great. I don't think there is anything that needs to change in this CL. One thing for us to ponder as team, there is some overlap in the JS interop used in this package and package:web. It may make sense for us to publish a node interop package so we can share this work. Perhaps some of our users may also want to use such a package.

Anyway, food for thought. Regardless, that is far outside the scope of this CL.

[devoncarew]

Thanks! cc'ing @mit for fyi on the PR; @athomas - do you mind doing a general review of this PR? It's substantially the same as the previous one (and trys to keep minimal diffs from the current bash impl).

[srujzs]

LGTM too!

[athomas]

LGTM, didn't review JS interop because people that know what they're doing already did :)

[athomas]

Just curious, why no package-ecosystem: pub?

[devoncarew]

I ran into some issues when eval'ing it when it was in beta (dependabot/dependabot-core#4979), and was generally waiting for them to be addressed before using the functionality more widely.

[devoncarew]

Thanks! PR updated.

[devoncarew]

I ran into some issues when eval'ing it when it was in beta (dependabot/dependabot-core#4979), and was generally waiting for them to be addressed before using the functionality more widely.