Remove virtual methods from MeshConnectivity in rendering

Virtual methods were used in the `MeshConnectivity` classes for the
internal ray casting system. However, using virtual methods in the
execution environment is being deprecated.

This change replaces the virtual object with an object containing a
`Variant`. The `Variant` holds one of the supported mesh connectivities
and selects the correct one at runtime rather than jumping into a
virtual method.
5 jobs for rendering-mesh-conn-no-virtual