Instead of storing build settings inside the language servers based on update notifications from the build system, always call into the `BuildSystemManager` to get the build settings.
Overall, I think this is a much clearer separation of concerns and will allow us to remove `SourceKitServer.documentToPendingQueue` in a follow-up commit as `SwiftLanguageServer` can always directly call into `BuildSystemManager` to get build settings and we don’t need to wait for the initial notification to receive the first build settings.
This requies `BuildServerBuildSystem` to keep track of the build settings it has received from the BSP server.
`ClangLanguageServer` still caches build settings locally. `ClangLanguageServer` will change to the same pull-based model in a follow-up commit.
The client guarantees that unsupported kinds will be handled, and in
practice some clients, such as Sublime's LSP plugin, use
`"codeActionKind":{"valueSet":[]}`, since they support all kinds anyway.
This behaviour was also clarified in a [spec issue
report](https://github.com/Microsoft/language-server-protocol/issues/620)
where it was confirmed the server can send any actions it wants. It
seems preferable to ignore it.
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.
