REFAC: ViewerVTK, RenderingVTK as Separate Libraries

See merge request iMSTK/iMSTK!711

REFAC: Interactor style and keyboard control refactor to fix dependencies, continued library reorganization

Upgrade to VTK 9.1

See merge request iMSTK/iMSTK!739

Improve build system to streamline application integration

See merge request iMSTK/iMSTK!702

The application of "vtk-8.2.cmake" patch was obsoleted by commit
f796986e (REFAC: VTK 9 and greater dependence, task graph timing
chart disabled, data replacements, example updates)

Consistently using "mark_as_superbuild" along side the declaration
of the associated option or cache entry facilitates maintenance by
helping ensure value are consistently passed to the inner build.

For example, it fixes the passing of these two options:

* iMSTK_ENABLE_CUDA_BACKEND: Introduced in 5e90bbce (ENH: Enable CUDA
  in CMake configuration)

* iMSTK_SWIG_PINNED_ARRAY: Introduced in c2b5429e (ENH: add pinned array;
  add cmake option to choose between marshal array and pinned array)

Unless option have to be passed using the command line, this is the
recommended approach to pass options. It avoids "command line length issues".

This commit sets the cache variable prior configuring the outer
build (SUPERBUILD=ON) and it makes sure it is also propagated
down to the inner project.

This commit sets the cache variable prior configuring the outer
build (SUPERBUILD=ON) and it makes sure it is also propagated
down to the inner project.