Completely deprecate virtual methods
Deprecate VirtualObjectHandle
and all other classes that are used to
implement objects with virtual methods in the execution environment.
Additionally, the code is updated so that if the
VTKm_NO_DEPRECATED_VIRTUAL
flag is set none of the code is compiled at
all. This opens us up to opportunities that do not work with virtual
methods such as backends that do not support virtual methods and dynamic
libraries for CUDA.