No `EnvironmentDescription::hasProperty` method

[ptheywood]

Unlike AgentDescription, which provides methods to check if an agent description has alreadyu been created a new Varaible by its' string name, Environment does not have a corresponding hasProperty method.

It can be checked with a try catch around a call to getProperty, but a bool returning version would be good for concistency with AgentDescription.

https://github.com/FLAMEGPU/FLAMEGPU2/blob/4e0260476353710860a4c29c7bd96da27c80aa05/include/flamegpu/model/AgentDescription.h#L134-L138