Implement SwiftUI-idiomatic Table APIs

[jverkoey]

Following https://developer.apple.com/documentation/swiftui/table.

The current implementation of the Table types are meant only to provide 1-1 mapping of W3C table types. Ideally Slipstream would provide an implementation of Table that's more idiomatic to SwiftUI too though, i.e. supporting data objects and typed column/row blocks.