Benchmark QFuture / QtConcurrent vs. Parallel STL

Extend the framework developed in QTBUG-131828 to run the same work sets not only in sequential and QtConcurrent-parallel mode, but also use parallel STL (https://en.cppreference.com/w/cpp/algorithm#Execution_policies).

If QTBUG-131829 was implemented: this tasks makes the benchmark results a 4d scalar field, so the visualization probably needs to be extended to create slices in the data set, e.g. comparing STL vs. Qt instead of 1...N-parallelism.