GH-1279: Improve the implementation of in-memory, general-purpose,non-transactional graphs.

- new module: jena-benchmarks, with two sub-modules:
  - jena-benchmarks-shadedJena480
    - This module wraps some dependencies from the Apache Jena Release 4.8.0
    - The wrapped module is used to implement regression tests against older releases
  - jena-benchmarks-jmh
    - contains JMH benchmarks for different Graph operations
      - Allows for the comparison of the performance of different Graph implementations and different releases of the same implementation
    - contains JMH benchmarks for SparseArraySpliterator and SparseArraySubSpliterator
29 files changed