Add better support for SPDX headers

[Seelengrab]

This commit does these things:

• Add rudimentary detection of EUPL-* licenses
• Add logging statements throughout the action to make it debuggable should some license not be properly detected
• Fix a bug with SPDX header detection in existing files

To expand on the last point - previously, the header detection didn't have multiline matching enabled on its regex, which meant that any file having any lines other than the SPDX header wasn't detected as actually having a header. That's a bit bad, since presumably there would be actual source code following that header.

For a visual example, before:

After:

As for tests - I looked at test/requests/test_actions.jl and found an extremely minimal test for that action. I have no idea how to add a test for the functionality there, so I'd appreciate any guidance you can offer.

For every PR, please check the following:

• End-user documentation check. If this PR requires end-user documentation in the Julia VS Code extension docs, please add that at https://github.com/julia-vscode/docs.
• Changelog mention. If this PR should be mentioned in the CHANGELOG for the Julia VS Code extension, please open a PR against https://github.com/julia-vscode/julia-vscode/blob/master/CHANGELOG.md with those changes.

[Seelengrab]

Since this bumps compat to 1.3 for the artifact, the failure on <1.3 is entirely expected - I hope this can still go through in some form, either actually dropping support for <1.3 or in some manner that allows better detection of licenses other than MIT.

[pfitzseb]

Unfortunately we're fairly committed to keeping 1.0 compat for now.

So, while being able to identify the license is probably useful, I think just fixing the regex is probably best for now. Also cc @fredrikekre because I think he originally implemented this?

[Seelengrab]

That's unfortunate to hear, especially since 1.0 has been out of language support for 2+ years now. I'd have loved to do some PRs with other code actions, but I don't really want to go back to the time of slow compilation :) Maybe this can be done with the next LTS?

I'll adjust the PR so only a very minimal version is done. Specifically:

• Fixing the regex, so the SPDX header is identified correctly
• Logging
• Adding detection of EUPL licenses the way it's done for MIT

[Seelengrab]

I've removed the artifact & compat bumpage, does this need anything else?

[pfitzseb]

Nope! Thanks again for the fix.

[Seelengrab]

Thank you!

[fredrikekre]

I'd have loved to do some PRs with other code actions

I think it is fine to have some actions behind a version check so don't let the Julia 1.0 support discourage you.

[pfitzseb]

Yes, but that's a bit tricky when it comes to dependencies.