Java: avoid call to Location.toString()

[nickrolfe]

Before

Most expensive predicates for completed query ExposeRepresentation.ql:
        time              | evals |   max @ iter | predicate
        ------------------|-------|--------------|----------
                    25.5s |       |              | Location#77b33c41::Location::toString#0#dispred#ff@7deb228l
                     6.3s |    75 |  2.1s @ 2    | ControlFlowGraph#5d746fff::ControlFlowGraphImpl::last#3#fff@f442bw2o

As well as being slow, this inserted the toUrl of every location into the string pool.

Evaluated non-recursive predicate Location#77b33c41::Location::toString#0#dispred#ff@7deb228l in 25496ms (size: 12294704).
Evaluated relational algebra for predicate Location#77b33c41::Location::toString#0#dispred#ff@7deb228l with tuple counts:
        12294704  ~0%    {2} r1 = SCAN Location#77b33c41::Location::hasLocationInfo#5#dispred#ffffff OUTPUT In.0, toUrl(In.1,In.2,In.3,In.4,In.5)
                         return r1

After

Most expensive predicates for completed query ExposeRepresentation.ql:
        time             | evals |   max @ iter | predicate
        -----------------|-------|--------------|----------
                    6.6s |    75 |  2.2s @ 2    | ControlFlowGraph#5d746fff::ControlFlowGraphImpl::last#3#fff@f442bw2o