Instead of listening for document updates sent from `sourcekitd` and sending a `PublishDiagnosticsNotification` based on the `sourcekitd` notification, wait for a little while and then execute an internal `DocumentDiagnosticsRequest` to load diagnostics and send them to the client.
This has two advantages:
- It unifies the two diagnostic implementations
- It removes the need to keep track of semantic diagnostics in `SwiftLanguageServer`
- It gets us one step closed to opening and editing documents in `syntactic_only` mode. The only thing that is left now are semantic tokens.
Add `.swift-format` to the repo and format the repo with `swift-format`.
This commit does not add any automation to enforce formatting of sourcekit-lsp in CI. The goal of this commit is to get the majority of source changes out of the way so that the diff of actually enforcing formatting will have fewer changes or conflicts.
