Allow archiving test artifacts

[award999]

To help diagnose test failures it would be handy to be able to archive test artifacts such as all the *.log files that the Swift extension produces. https://github.com/actions/upload-artifact works well and is MIT. It would be nice to put this in the common test workflow as a step after the test step, and have a variable that allows downstream jobs to configure the glob patterns to archive.

[award999]

cc @shahmishal. Any problem with me doing this? Now that the Swift extension is producing diagnostic log files (swiftlang/vscode-swift#1746), it would be nice to archive them to diagnose test failures.