* Adding tests for CMP0118 being unset (aka set to `WARN`).
* Adjusting the (unrelated) RunCMake.CMP0026 test to set CMP0118 to
  `NEW`,
* Adjusting the (unrelated) RunCMake.Ninja test to set CMP0118 to `OLD`.
* Adjusting the (unrelated) RunCMake.FileAPI test to set CMP0118 to
  `OLD`.

Note:
Setting CMP0118 to `NEW` and modifying the `GENERATED` property with
`set_property` or `set_source_files_properties` will currently NOT set
that property because the implementation is still to come.