Add a CI config to check formatting and run tests

[ademuri]

This uses Github Actions to run deno fmt --check and then ./make.js test. It also configures deno fmt to ignore the icon SVGs, and changes the DOM tests to launch Puppeteer with --no-sandbox.

[philc]

Thanks for the PR. What was your motivation for adding the workflow?

I'm concerned maintaining the configuration adds more moving parts than it's worth -- I haven't experienced much pain resulting from broken tests or unformatted code in PRs for this project.

Why is make.js reformatted in this PR? The version in master looks correctly formatted.

Great idea to exclude svgs from deno's fmt check.

[ademuri]

I'm not sure why make.js was re-formatted - I reverted that change.

I read your contributing guide, and thought that since reviewer time is relatively scarce, this would be helpful. This also makes contributing easier, as for small changes authors don't necessarily need to install the build environment locally to get test results. The maintenance burden for this config is low, and I'm happy to own fixing any breakages. If anything breaks, it's easy to ignore or disable.

Checking that formatting is applied at each commit helps keep diffs/blame clean, rather than requiring specific formatting commits. If you're amenable, I can submit a pull request to add a commit hook to run deno fmt on commit, so that formatting is automatically applied.