C++: move logic from DefaultTaintTracking into TaintTrackingUtil

[rdmarsh2]

No description provided.

[jbj]

The code LGTM, but how do you plan to ensure that performance is good on real snapshots? The new additions are essentially dead code until we can retarget DefaultTaintTracking to use TaintTracking or until we write queries directly on TaintTracking.

[rdmarsh2]

I had planned to modify DefaultTaintTracking to use some of the TaintTrackingUtil predicates, but the semantics don't quite line up:

• I didn't copy the pointer/object conflation that DefaultTaintTracking does for modeled functions. I think C++: Wire up param/arg indirections in data flow #3123 will make that unnecessary, but I'll add it for the moment.
• the existing taint steps in TaintTrackingUtil don't use the predictability constraint that DefaultTaintTracking has. I think that's a change we want to make eventually, but it's a big/scary change, and I don't think I can have DefaultTaintTracking use TaintTracking::Configuration without making it.

I'll go ahead and do those, but make the latter change on a separate branch

[jbj]

On balance, I prefer merging this code now rather than later. It seems better to have dead code merge than to have it sitting in a PR.