We don’t have any guarantees which thread these blocks will be called on by sourcekitd, so we shouldn’t make any assumptions about it in Swift. We should thus mark them as Sendable.
This adds a sourcekitd plugin that drives the code completion requests. It also includes a `CompletionScoring` module that’s used to rank code completion results based on their contextual match, allowing us to show more relevant code completion results at the top.
Naming types in sourcekitd_functions.h `sourcekit_api_` instead of `sourcekitd_` indicates that these are types to be used with dynamically loaded sourcekitd libraries. It avoids confusion if sourcekitd is also linked, which adds the `sourcekitd_` symbols.
Adding nullability annotations to it is also just nice.
And some improved formatting never hurts.
