Merge topic 'imported-implib-only'

7351d590ee cmTarget: Add a way to represent imported shared library stubs
83574a4772 GeneratorExpression: Expand testing of imported location resolution
b75ff51947 Testing: Map RelWithDebInfo config in GeneratorExpression test

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: Jason Juang <jasjuang@gmail.com>
Merge-request: !8582