Expose the Render* members to public

[klepto2]

While this might not be needed for most users, and a lot can change in the Render* classes can change.
It is needed to have access to have access to this classes from its highlevel counterparts. (eg: Texture -> RenderTexture)

Why:

• More flexibility
• Easier to add extensions which require low level access like GLHandles or VK handles depending on the renderer
• Integration of third party things will be easier.

I noticed that there were some kind of methods to get this data. Like the commented Ultraengine::Render::GetRenderTexture function. something like this for all Render* items would be nice.