Merge topic 'ctest-resource-fixes' into release-3.16

a033bafbe0 Help: Clarify how tests are run if no resource spec file is specified
a64ba0235f CTest: Clarify that resource requirements can be split
f9f294f5fa CTest: Add version field to resource spec file

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !4080