This feature requires the user to add a command that generates a
`rust-project.json` from a set of files. Project discovery can be invoked
in two ways:
1. At extension activation time, which includes the generated
`rust-project.json` as part of the linkedProjects argument in
InitializeParams
2. Through a new command titled "Add current file to workspace", which
makes use of a new, rust-analyzer specific LSP request that adds
the workspace without erasing any existing workspaces.
I think that the command-running functionality _could_ merit being
placed into its own extension (and expose it via extension contribution
points), if only provide build-system idiomatic progress reporting and
status handling, but I haven't (yet) made an extension that does this.
