Swift for Linux support

[Mike-Gough]

As a developer building a static website using Publish, I'd like to be able to import this Plugin and use it in my build pipeline. However, JavaScriptCore is not available on Linux and this causes the following exception to be thrown:

/mnt/c/git/mike.gough.me/.build/checkouts/highlightjspublishplugin/Sources/HighlightJS/HighlightJS.swift:1:8: error: no such module 'JavaScriptCore'
import JavaScriptCore
       ^"
Output: ""

Is it possible for this plugin to log a warning if this framework is not available rather than throw an exception?

This would enable developers to prototype their websites on a Linux machine, or a Windows machine via WSL, but still enable them to build and publish the final product on a mac via something like github actions.