add render task to layer.
entities layer.
needed render target. Do not change if previous target was the same.
Optional
subGeoms: Vector<string>if specified: only sub geometries from this list will be rendered.
return render rask render target, by render task index. Throw if index >= tasks size.
render task index.
task render target
A list of render task. Every task consist of entites layer to draw, render target in which draw, and optional list of sub geomteries names. Cannot be changed after effect activation.