Use Result type for returning success result or error

[FZambia]

Where we currently use void onDone​(@Nullable java.lang.Throwable e, @Nullable T result).

Similar to Result type we use in our Swift SDK. Or similar to kotlin.Result.

In Java it may be sth like this:

public class Result<T> {
    private T result;
    private Throwable error;

    private Result(T result, Throwable error) {
        this.result = result;
        this.error = error;
    }

    public static <T> Result<T> success(T result) {
        return new Result<>(result, null);
    }

    public static <T> Result<T> error(Throwable error) {
        return new Result<>(null, error);
    }

    public T getResult() {
        return result;
    }

    public Throwable getError() {
        return error;
    }

    public boolean isSuccess() {
        return error == null;
    }

    public boolean isError() {
        return error != null;
    }
}

For now opened to collect opinions, unfortunately this will break API.