Async Shim instead of "syncable" protocols

[avaidyam]

PSE (rather, ParrotServiceExtension) should only support pure async methods. Parrot (client-side), there should exist a set of async --> sync shims. For example:

public protocol AsyncProtocol {
    func getProperty(_ reply: (Any) -> ())
    func setProperty(_ value: Any)
    
    func doThing(_ input: Any, reply: (Any, Error) -> ())
}

public struct SyncShim {
    var property { get set }
    func doThing(_ input: Any) throws -> Any
}