Apply the following changes:
- Check for the presence of `#Playgrounds` textually before getting the module name in `SwiftPlaygroundsScanner`. This is important because getting the module name requires us to get build settings for the file, which can be expensive. Do the cheaper check first
- Make `syntacticTests` and `syntacticPlaygrounds` closures capture the workspace instead of passing the workspace from the `SwiftSyntacticIndex` back out. I like this better because now we can’t accidentally pass the wrong workspace to a `SwiftSyntacticIndex`, eg. to `buildTargetsChanges`.
- Capture the initialize result in `TestSourceKitLSPClient` instead of using `postInitialization` to capture the result
- Minor cleanup of unnecessary abstractions, likely artifacts of earlier iterations
- Restructure tests so that every test has its own list of source files, allowing for easier local reasoning – turns out some of these tests didn’t even need to open a workspace, just to check the initialize response
