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.
The `ImplicitFunction` classes are now trivial classes that can be
passed among host and devices. Because of this, we now need to know the
type of the `ImplicitFunction` in order to use it.
The old functionality still exists (when virtual methods are still being
compiled), but will give deprecation warnings. It is also not possible
to get a pointer from `ImplicitFunctionHandle` and cast it back to the
original data type (because the type changed). This is a weird testing
feature that makes little sense in practice.
Also unsupported in the deprecated classes is the ability to change
the object and have those changes reflected in the handle. This is
unfortunate, but it would have been difficult to implement this
feature that is going away and only appears to be used in some of
the tests.
Marked the old versions of PrepareFor* that do not use tokens as
deprecated and moved all of the code to use the new versions that
require a token. This makes the scope of the execution object more
explicit so that it will be kept while in use and can potentially be
reclaimed afterward.
Now that the dispatcher does its own TryExecute, filters do not need to
do that. This change requires all worklets called by filters to be able
to execute without knowing the device a priori.
