This mechanism sets up CMake variables that allow a user to select which
modules/libraries to create. Dependencies will be tracked down to ensure
that all of a module's dependencies are also enabled.
The modules are also arranged into groups.
Groups allow you to set the enable flag for a group of modules at once.
Thus, if you have several modules that are likely to be used together,
you can create a group for them.
This can be handy in converting user-friendly CMake options (such as
`VTKm_ENABLE_RENDERING`) to the modules that enable that by pointing to
the appropriate group.
The circular dependency came from UnknownArrayHandle.h needing
VTKmDefaultTypes.h, which needed all the cell set types. Some of those
cell sets used ArrayCopy in templated functions. Changed those functions
to directly deep copy the ArrayHandle.
There was an error that caused deprecation warnings in VTK-m to be
suppressed, which meant that many uses of deprecated features went
unnoticed. This fixes those deprecation warnings.
The majority of the warnings were caused by the use of the deprecated
`Cast`, `CopyTo`, and `ResetTypes` methods of `UnknownArrayHandle` (or
`VariantArrayHandle`). Both `Cast` and `CopyTo` have been subsumed by
`AsArrayHandle` (to make the functionality more clear). `ResetTypes` now
requires a second template argument to define the storage types to try.
Also fixed some issues with `SerializableField` being deprecated.
This class is no longer necessary because `Field` can now be directly
serialized.
