Add support for Windows

[punya]

Fixes #1

[ryandens]

Ideally this would include an automated job that runs a build on windows github action - I admit I don't use windows for development so not sure the best way to approach this. Very open to changes in the plugin build and the plugin to enable both to work seamlessly on windows machines. Mostly, I'm concerned about accidentally introducing a future change that breaks windows without me having a way of knowing about it.

[punya]

CI failed on macOS:

> Task :plugin:functionalTest

com.ryandens.javaagent.JavaagentPluginFunctionalTest > can attach to application run task FAILED
    org.gradle.testkit.runner.UnexpectedBuildFailure at JavaagentPluginFunctionalTest.kt:227


8 tests completed, 1 failed
> Task :plugin:functionalTest FAILED

...but I can't reproduce this locally on macOS. I think this might be a flaky test (I saw it fail in this way once and then pass again).

[ryandens]

Huh, that's interesting. I activated the build scan from that build, and it looks like the simple-agent jar is not present at the time that test executes 🤔 https://scans.gradle.com/s/lu7fzdilc6rlq/tests/overview