jextract: Move Foundation support into a common package

[sidepelican]

• Addresses Move Foundation support into a common package #638.

Instead of generating Date, Data, and DataProtocol implementations within each user module, I will bundle these as part of SwiftJava's standard library.

Fixed implementations are now located under org.swift.swiftkit.core.foundation and org.swift.swiftkit.ffm.foundation.
Removed printSpecificTypeHelpers from the code generation process.

This ensures that when multiple modules utilize swift-java, they all share a single, unified set of Foundation classes.

[ktoso]

Very nice, let's add some docs onto it that this is Foundation.Data and link to https://developer.apple.com/documentation/foundation/data

[ktoso]

Hmmm on the other hand, shouldn't this be generated? We can use the jextract --single-type mode perhaps and point it at https://github.com/swiftlang/swift-foundation/blob/main/Sources/FoundationEssentials/Data/Data.swift

We should have some script in scripts/ (there's a few, maybe one of them) that does that and generates this file perhaps? We can use the filterInclude to pick which exact pieces of Data we want etc

[ktoso]

Ah damn we can't because we're adding helper methods to it...

We'd need an extra feature to "add extra methods to imported type"... that would be great though 🤔

[ktoso]

Same as on the other type; can we find a way to generate those using a script and not just by hand paste the generated code?

[sidepelican]

I actually tried that approach at first, but I ran into quite a few minor issues.
It needs more custom logics into the generater.
Since Date and Data had their own dedicated code generation logic (printSpecificTypeHelpers), I thought it would be easier to manage the source code manually rather than dealing with the maintenance overhead of the generator.

[sidepelican]

I'll look into code generation a bit more

[ktoso]

Thank you!

I think we maybe we need some extra setting that is "sourceGenAdditionalMembers" { "MyType": "Sources/Something/Data+Extras.java" } } or something...? And we'd just "plop" those sources into the generated java type maybe? (silly names, we can think of better ones)