Support subscript APIs. E.g. ```swift public struct MySwiftStruct { public subscript(x: Int) -> Int { get set } } ``` `subscript` accessors can be modeled in `ImportedFunc` as `.getter`/`.setter` with parameters, or new `SwiftAPIKind`.
Support subscript APIs. E.g.
subscriptaccessors can be modeled inImportedFuncas.getter/.setterwith parameters, or newSwiftAPIKind.