Cleanup: Collection of cleanup tasks

[hannojg]

☑️ Cleanup useDisposableResource

The function should accept:

• simple, non async, creation functions
• worklet functions, which automatically get executed on the worklet thread

☑️ Cleanup: EntityWrappers should use adoptEngineRef

• EntityWrappers should become releasable
• When an entity gets deleted engine->destroy should be call, thus call EngineWrapper creators should create an entity using adoptEngineRef
• Make sure this causes no weird side effects, like only locally in a function scope creating an entity, and then it gets deleted while it was still added to a scene etc

☑️ Cleanup: All functions creating custom geometry should return a VertexEntity

This is needed because otherwise we leak the vertex buffers (note: the engine implementation is so nice to clean it up for us, but its better if we are explicit about it)

• Instead of returning EntityWrapper, return VertexEntity
• EntityWrapper should accept optional shared pointers to vertex buffers (thus holding them)
• On release the vertex buffers should be deleted as well

☑️ Cleanup: MaterialInstance and Material should have same methods in regards to parameters