Instancing benchmark demo

[smlpt]

This PR adds a benchmark to the Demo > Advanced menu. It allows you to compare the conventional means of node publishing with instanced geometry, using spheres as objects. The benchmark type can be run in four ways:

• publish each node separately
• publish all nodes cumulatively at the end
• populate the scene with instanced geometry sequentially
• populate the scene with instanced geometry using a parallel stream over the array, which is even faster

There are also parameters for the number of (instanced) particles (defaults to 1000) and the spread in each dimension.

[kephale]

One concern I have is that if a user doesn't know what to expect when running this, they could have a pretty bad time (e.g. if they run the addNode publish all with too many agents then it will get stuck).

Maybe some kind of warning in the Command dialog itself that they should be cautious, it could freeze their application, etc..

[smlpt]

That's a good point. I added a label with approximate timings:

[kephale]

The last requests would be:

• mentioning this benchmark in the docs like @ctrueden suggested
• add a Gradle usage example in the docs

[smlpt]

Added a benchmarking page to the docs and registered a gradle task to run the benchmark from a CLI.

[smlpt]

@skalarproduktraum done 👍