Adds RunPlanVector::setPropertyStep()

[Robadob]

This has behaviour similar to Python's range(), more appropriate than lerp in many cases with integers.

Providing this will hopefully help people avoid using lerp wrongly for integers.

https://github.com/FLAMEGPU/FLAMEGPU2-docs/pull/175

alt possible names:

• setPropertyUniformStep()
• setPropertyInterval()
• setPropertyUniformInterval()
• setPropertyRange() (reminds me of Python's range() although it's not 1-1 as the length is predefined).

[Robadob]

I've ran both tests Windows.