Improve mutant naming

[dupdob]

Is your feature request related to a problem? Please describe. As of today, mutant naming is inconsistent in Stryker.Net (note that I probably contributed to that), there is a liberal of use of mutants and mutations as being one and the same. On a similar topic, I have never been satisfied with the status 'CompileError' which sounds far too technical.

Describe the solution you'd like I propose to adhere to stricter guidelines:

• a mutation should refer to individual mutations that Stryker generates thanks to mutators?
• a mutant should refer to a variant of the original project with at least one mutation.
• a mutated assembly is a variant of the original assembly integrating several mutations that can be individually activated.
• a mutation that cannot be tested because it triggers compilation error(s) should be flagged as 'Non viable*

In general, I propose we adhere to whatever de facto standard appears to exist. Pitest comes to mind, but I let you decide which source makes more sense if any.

Agreeing to these rules or some alternative would allow to review and clean up existing logging entries and messages to make them most consistent. They should also be added to the contribution guidelines, of course.

[rouke-broersma]

The mutant states are described here and they are shared by all stryker frameworks, changing CompileError to Non Viable is something we have to discusss with the rest. In principal I do not disagree, but we cannot decide to make this change by ourselves.

The rest of the definitions you outlined IMO are already the definitions we would (like to) use, but yes we are probably way too inconsistent. It would be a good idea to describe them in the docs.

[rouke-broersma]

@stryker-mutator/stryker-net @stryker-mutator/stryker-js-and-friends @stryker-mutator/stryker4s Thoughts?