This required changing our approach to OS prompts and this commit greatly
simplifies that. We now avoid passing a callback and return a simple future
instead. This lets callers spawn tasks to handle those futures.
When bundled, we will retrieve it out of the `Resources` folder.
Locally, we're expected to run `script/download-rust-analyzer` and
put `vendor/bin` in our $PATH.
Nathan Sobo
Antonio Scandurra
Max Brunsfeld