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It isn't part of VTK's public interface.

This helps to find packages that VTK itself needs by adding additional
locations to `CMAKE_PREFIX_PATH`. The hard work goes into figuring out
which prefixes to add.

This allows ParaView to easily replicate VTK's package.

In the long run, it would be nice to have exported module targets be
part of a namespace. However, the logic assumes that module names are
targets as well. There needs to be some way to find out the target name
of a module and use it instead of the module name in various locations.

Testing within an example is currently broken. Investigation is
necessary.

Some third party packages do not work properly with this setting, so
exclude them for now.

This is so that there is a place to insert new logic for the new module
system.