When encountering an `#include "<PATH>ui_<BASE>.h"` statement,
search for `<BASE>.ui` in
 - <SOURCE_DIR>/<BASE>.ui
 - <SOURCE_DIR>/<PATH><BASE>.ui
 - <AUTOUIC_SEARCH_PATH>/<BASE>.ui
 - <AUTOUIC_SEARCH_PATH>/<PATH><BASE>.ui

In CMake 3.8.2 the lookup list was
  - <SOURCE_DIR>/<BASE>.ui

In CMake 3.9.[01] the lookup list was
 - <SOURCE_DIR>/<PATH><BASE.ui>
 - <AUTOUIC_SEARCH_PATH>/<PATH><BASE>.ui

Closes #17168