Change lua test files to call `require 'lldebugger'` only when using
love, because it's not needed with lua or luajit. Also add `stopOnEntry`
key to test `.vimspector.json` because it works correctly with this
change.
Change Dockerfile to install lua, luajit and love and also to install
nodejs 12 needed to build the lua debug adapter. Create the
love-headless test in support/test/lua to test love without an x server.
