This was the minimal amount of predicates I could easily cache without
introducing extra cached stages. The predicates that are not cached
here, like `CppType::getTypeSize` and `getCanonicalLanguageType`, appear
to be cheap.
I've tested that this avoids recomputation of the IR type system by
running
grep -c 'Starting to evaluate predicate CppType::CppType::getIRType_dispred'
on the evaluator log for `IRSanity.ql`. It drops from 4 to 1. The
pretty-printed DIL drops from 79,175 lines to 76,326 lines.
fb4dac597c