[NFC] Make Precompute use a lazy LocalGraph

[kripken]

To do this, add locations and getInfluences to LazyLocalGraph. Both cannot
really be computed in a fine-grained manner, so just compute them all on the
first request. That is not as efficient as our lazy computation of getSets and
setInfluences, but they are also less important, and this change makes the
pass 20% faster.

[tlively]

Since the computation isn't lazy in a fine-grained way that pessimizes performance when all the information will be needed, would it make sense to compute these on demand for all LocalGraphs and not just lazy ones?

Other than that question, LGTM.

[kripken]

I think maybe not, since laziness has a cost, even if small. If you know you will definitely need getInfluences then the branch on "have I lazily computed them" is wasteful, even if it is well-predicted.