Evaluating Jsonnet File Action should not block

[zzehring]

Right now, evaluating a jsonnet file that takes a while to generate blocks the IDE, forcing the user to wait until the file is done evaluating. Ideally, this should be done asynchronously. Unfortunately, there's a chance this is an issue with the underlying libraries we use (like lsp4intellij), but we should see if there's something to be done.