jextract-swift support importing nested types

[ktoso]

We have some name look-up working for this already, but the source synthesis may also want to generate nested types for such.

[timofeys1]

Is this issue about cases like the following?

public class Foo {
    public class Bar {
    }
}

While testing #486 on some public libraries, I noticed that as of 5764bc2a1b706056121109dc0ab14fd3d771cbc5, these don't compile with errors like:

error: expressions are not allowed at the top level
 25 |
 26 | @_cdecl("swiftjava_getType_MySwiftLibrary_Foo.Bar")
 27 | public func swiftjava_getType_MySwiftLibrary_Foo.Bar() -> UnsafeMutableRawPointer /* Any.Type */ {
    |                                                 `- error: expressions are not allowed at the top level

[ktoso]

Yeah, it's about problems like these.

Sorry for slow reply, travel + got sick during it 🤧