Add engineStreamingGetUsedMemory

[Pirulax]

Function for retrieving the amount of memory (in bytes) used by the GTA streamer.

[Pirulax]

Maybe engineStreamingGetMemoryInUse is a more fitting? Or engineStreamingGetMemoryUsed?

[AlexTMjugador]

I'd suggest engineGetStreamingMemoryUsed, because most engine functions follow the naming convention of engine + verb + object, so it's arguably more consistent. But your choice is as good as mine 😄

[Pirulax]

It is more consistent, but I want to add more streaming functions in the feature, so I thought that placing streaming after engine might make those functions more consistent.