Handle default parameter in cloneFunction

`vibe.internal.meta.codegen.cloneFunction` didn't take default parameters into account.
This prevented the REST generator for providing default parameter for client, e.g:

````
@rootPathFromName
interface ITestDefaultParamGet {
    string getRessource(string param = "42");
}
class TestDefaultParamGet : ITestDefaultParamGet {
    string getRessource(string param = "42") { return param; }
}

// Some code...
    auto api1 = new RestInterfaceClient!ITestDefaultParamGet(LstURL);
    auto answer1 = api1.getRessource();
    assert(answer1 == "42");
````