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.
Workaround for SR-16097 to avoid hitting SR-16095: VSCode will send shutdown requests without a 'params' key. On macOS getting the superDecoder for a non-existent container returns an empty decoder, on Linux it throws `DecodingError.keyNotFound`, causing a crash.
Perform a targeted fix: If we don't have 'params' and the request is a ShutdownRequest, manually create a `ShutdownRequest` without any parameters.
rdar://91288093
* Replaces two logs since those don't result in response messages anymore
* Adds a func for sending messages synchronously, to get the two messages out before fatalError
