CPP: TlsSettingsMisconfiguration.ql performance and cleanup

[geoffw0]

This query was performing really poorly, due to some haphazard use of dataflow. This PR makes some improvements, not all of which are exactly behaviour preserving - but the tests are not affected, nor are results on any snapshot I've found.

[jbj]

The changes LGTM, but I think there is some more low-hanging fruit to pick. The from ... select contains lots of restrictions that I think could be moved into the isSource definition. A rule of thumb in data flow queries is that everything that can be phrased as a unary predicate on source or sink should be moved into isSource and isSink respectively.

Concretely, I think we want a predicate isProtocolSource(Expr protocolSource, ConstructorCall cc, Expr e, string msg), and isSource is then isProtocolSource(source.asExpr(), _, _, _).

[geoffw0]

Thanks for the suggestions - I will do a follow-up PR after this one is merged.

The main thing I wanted to fix here was ExistsAnyFlowConfig, which had source any() and sink any() before these changes - big red flag.

[jbj]

The qlformat check has failed.

[geoffw0]

Fixed format.