Implementation of the proposal in: #121535
When drawing with "project to surface" turned on, it is now possible to restrict the projection to only the selected objects.
This is really useful for drawing onto surfaces that has a lot of detail meshes that you don't want to project onto.
Performing an off-screen draw call while drawing the viewport isn't
supported, add a check that raises an exception when called from Python
instead of crashing.
Ref: !118780
Overall the transition to C++ in the draw module is awkwardly half
complete, but moving more code to a C++ namespace makes cleaning up
this code in other ways much easier, and the next C++ cleanup steps
are clear anyway.
