IoHost logger-only implementation

[mrgrain]

From the RFC implement a private CliIoHost class that satisfies the notify(...) method of the interface and required message interfaces.

interface IIoHost {
  /**
   * Notifies the host of a message.
   * The caller waits until the notification completes.
   */
  notify<T>(msg: IoMessage<T>): Promise<void>;
}

The implementation should follow the existing logging implementation. However this ticket will not change any existing functionality.

• You don't need to have an interface just the implementations.
• Create IoMessage except for the data property
• Add all code to new files into a new toolkit subdirectory in the cli package.
• None of these classes and files should be exported.