When the client supports it, communicate the structure of tasks that were stared during background indexing or by the build server to the client. If there are multiple operations happening in parallel, this allows the client to display them in separate log tracks instead of interspersing them with the emoji prefixes like we do today.
If the editor has support for this LSP extension, it can create a separate output view for the index log.
For example, in VS Code, we could have one output view for the standard LSP logging (which are the messages between VS Code and SourceKit-LSP if verbose logging is enabled in VS Code) and a separate log that shows information about background indexing.
rdar://128572032
Request types should always have the suffix Request and notifications
should end with Notification.
Also moved all request and notification types into separate folders to
reduce the number of files in the LanguageServerProtocol folder.
