Reduce calculation for fragments in ExecutableNormalizedOperation

[dondonz]

After parsing and validating an incoming GraphQL operation, the engine creates a normalized version of that operation, the ExecutableNormalizedOperation.

For fragments, there is a little more work involved to determine the possible types. Inside narrowDownPossibleObjects, there is a set intersection between the current set of possible objects and the set of types from the resolved type condition.

This set intersection can be expensive for very large queries with hundreds of fragments. This PR includes one such example.

In almost every case in the example query, one of the sets being compared only has one member. For example, the resolved types set often has only 1 member, because an inline fragment on a concrete type has only one possible type. It would be equivalent, and much cheaper, to calculate via Set contains rather than intersection.

And I've added a more general tweak to always pass the smallest set first to Guava's Sets.intersection. The implementation is faster when the first set is smaller.

Benchmark results

Baseline

Benchmark                                 Mode  Cnt    Score    Error  Units
NQExtraLargeBenchmark.benchMarkThroughput  thrpt    9  274.744 ± 14.909  ops/s
NQExtraLargeBenchmark.benchMarkAvgTime      avgt    9    3.658 ±  0.310  ms/op

Optimised

Benchmark                                 Mode  Cnt    Score    Error  Units
NQExtraLargeBenchmark.benchMarkThroughput  thrpt    9  333.346 ± 25.986  ops/s
NQExtraLargeBenchmark.benchMarkAvgTime      avgt    9    2.905 ±  0.124  ms/op

Note: For throughput, a higher number is better. For average time, a lower number is better.

[bbakerman]

Java shits me on how access to a first member is that god awful collection.iterator().next()

But here we are!

[bbakerman]

Perhaps create a utitlity method in graphql.util.FpKit

FpKit. intersection( that does this optimisation for same type sets

[dondonz]

That's a good idea I'll stick it in FpKit instead

[bbakerman]

Add tests for the new intersection method

[bbakerman]

There should be a test for this. I know its simple. So lock it in with a test