Ability to enable/disable may_race checks per race digest

[michael-schwarz]

Closes #1664.

[sim642]

This was useful for experiments, but those are now done I guess.

I'm wondering how much sense it makes to keep this extra configurability for the future. What this allows is having some analysis active but not using the information it computes to exclude races — a feature that no user would ever want.
It also creates a huge opportunity for misunderstanding and misconfiguration: the options are enabled by default, which makes it seem like all of the features are being used when in fact they are not. Only some of us would know that they do nothing unless some corresponding analysis is also activated. Having the defaults flipped wouldn't be any better: one might then try to enable them without effect or try to activate some analysis without effect.

The race digest experiments are tagged anyway and these changes could easily be cherry-picked for future experiments if really necessary.

[michael-schwarz]

Closing as this is included in #1666 which we'll keep open until we have cut the artifact release from it. A separate PR is not needed.