Add ability for interactive control of sim execution

[chili-chips-ba]

ModelSim has a really handy Tcl console from which users can command simulation start and stop, create break points, and otherwise interact with sim in a way that facilitates debug. Such ability is of great value, and @wyvernSemi's VProc has the potential for adding it to the opensource tools.

While we intend to bring it to life within Wireguard project, we also believe it would be of interest for the wider community to have it. A corresponding Feature Request is therefore filed for Verilator.

When in comes to interactive and incremental waveform viewing, we doubt that GTKWave has a workable solution. The Surfer however may be more amenable to it. Here is the relevant discussion track.