Merge topic 'optional-dep-imported-check'

d8daedb6 Testing/External: remove _PACKAGE variable setting
eed181b8 vtkModule: fix the "needs _FOUND" check for optional deps
955f6e65 vtkModule: fix sample command name
2cfff6f9 vtk-config: implicitly search for all components when none requested
4ecb9314 Rendering/RayTracing: fix target checks for optional dependencies
7725bf8a Filters/Parallel/Testing: fix `pvtkpython` check

Acked-by: Kitware Robot <kwrobot@kitware.com>
Tested-by: buildbot <buildbot@kitware.com>
Reviewed-by: Mathieu Westphal (Kitware) <mathieu.westphal@kitware.com>
Reviewed-by: Spiros Tsalikis <spiros.tsalikis@kitware.com>
Merge-request: !10972