Cannot access SettingPresets when XcodeGenKit is used as a library.

[mtj0928]

I'd like to use XcodeGenKit on my project as a library. However, Bundle.main is used here. https://github.com/yonaskolb/XcodeGen/blob/f65dad76252a876eae19ce72ea3649f95401e084/Sources/XcodeGenKit/SettingsBuilder.swift#L187

Bundle.main works well when we use XcodeGen as an executable target, but it doesn't work when we used XcodeGenKit as a library.