We currently load the entire package before generating a `SwiftPMBuildSystem`. That means that the initialize request to SourceKit-LSP is blocked until the package has been loaded, preventing us from offering any sort of functionality, including syntactic functionality like formatting.
Decouple build system creation and build graph generation (aka. package loading for SwiftPM). We can operate with fallback build settings until the build graph has been loaded and reopen the document once the proper build settings are available.
rdar://126644596
Do one of the following for every `FIXME` or `TODO` comment
- Add an issue that tracks the task
- Remove the comment if we are not planning to address it
