Implement simple terminal emulator as an alternative to GUI

[edigaryev]

In Tart, the primary way to interact with the VM is using the GUI abstractions provided by the Virtualization.Framework, namely, VZVirtualMachineView.

However, there's no such thing in Cloud Hypervisor. The best we can expect at this moment is an I/O access to the VM's serial port and/or virtio-console.

Piping these I/O streams to the standard input/output results in very poor UX, because it becomes impossible to terminate the VM with Ctrl+C as this keystroke is intercepted and routed to the VM instead by the terminal.

What we can do to fix this is to implement something like Minicom, but only offer the following functionality:

• ability to terminate the VM using some pre-determined escape-sequence

Optionally, nice to have:

• allow switching between the serial console view and virtio-console view, similarly to how tmux achieves multiplexing