feature: LSP (Language Server Protocol) support

[jbergstroem]

Couldn't find an open issue tracking this, so I went ahead. It would be awesome to have actionlint act as a LSP; similar to golsp; but for github actions. This would improve latency and interactivity across all IDEs.

One way to start could be by using the language protocol implemntation from golsp: https://pkg.go.dev/go.lsp.dev/protocol

[rhysd]

How about efm-langserver? I think it's not hard to write up a pattern to match error messages from actionlint -oneline.

The regular expression of problem matcher and a script to generate the matcher may be helpful to understand the structure of error message.

[jbergstroem]

Didn't know it existed. Will check it out!