Statix: support for traces and term depth configuration

[AZWN]

In order to debug Statix specifications, it would be useful to be able to control the stack trace length and the term depth of the messages that are generated.

[Gohla]

@AZWN In Spoofax 2, this is configurable per-project right? We do not yet have project-specific settings in Spoofax 3, and this is something that I want to spend some design time on to get it right in Spoofax 3. Would it be fine for now to have this configurable per-language, and overridable per-project in the future? And what do you think the defaults should be?

[AZWN]

Yes, a per-language solution would be fine for now. The Spoofax 2 defaults are: 0 for stack trace length, and 3 for term depth.

[Gohla]

Implemented in 21fc3f3