This is an implementation of `textDocument/definition` request.
Supports types only, and only in case when type is found in Zinc Analysis. When source(s) are found then editor opens potential source(s).
This simple implementation does not use semantic data.
During the processing of `textDocument/didSave`, we will start collecting the location of Analysis files via `lspCollectAnalyses`.
Later on, when the user asked for `textDocument/definition`, sbt server will invoke a Future call to lspDefinition, which direct reads the files to locate the definition of a class.
This is the first cut for the Language Server Protocol on top of server that is still work in progress.
With this change, sbt is able to invoke `compile` task on saving files in VS Code.
This implements JSON-based port file. Thoughout the lifetime of the sbt server there will be `cwd / "project" / "target" / "active.json"`, which contains `url` field.
Using this `url` the potential client, such as IDEs can find out which port number to hit.
Ref #3508