Move Foundation support into a common package

[sidepelican]

Currently, Foundation.Date support is generated locally within each package.
This creates duplicate classes like com.packageA.Date and com.packageB.Date when multiple Swift packages use swift-java, which is confusing on the Java side.

Moving Foundation support into SwiftJava (along with SwiftKitCore and SwiftKitFFM) would solve this problem.
The implementation is small, so I think this will have minimal impact.