A few implementations of Render() contain const-casts nested within its
their call hierarchy to get around the fact that this function is marked
const. We can just make the member function non-const to allow removal
of these casts in follow up changes.
Previously the std::move calls wouldn't do anything, as the parameters
were constant references, so we can take them by value and move into the
constructor and then move the parameters into the member variables.
While we're at it, we can initialize the vectors in place instead of
constructing and then assigning to them.