Add support for Eclipse Target Communications Framework (TCF)

[Joel Sherrill]

This ticket is to track adding RTEMS support for the Eclipse TCF. From ​https://www.eclipse.org/tcf/:

• TCF is a lightweight, extensible network protocol for driving embedded systems (targets).

• On top of the protocol, TCF provides a complete modern debugger for C/C++ and Ada, as well as the "Target Explorer" for system management. TCF works out of the box for Intel, PPC and ARM Linux targets including the Raspberry Pi. It supports Proxying and Tunneling for IoT devices, and is particularly strong for multi-process debugging even with slow communication links.

There is an implementation of the agent which is under an appropriate license. It is available from ​https://git.eclipse.org/c/tcf/org.eclipse.tcf.agent.git.

This likely needs to be supported in a manner that does not duplicate code with libdebugger but leverages it. TCF appears to support more than debugging though. Part of this ticket will be to identify what features need to be supported and how to enable them.