Target-based qt6_add_resources doesn't handle -binary option like qt6_add_binary_resources

Resulted from public CMake API discussion at https://codereview.qt-project.org/c/qt/qtbase/+/317353/1/src/corelib/Qt6CoreMacros.cmake#309

Users might want to create standalone compiled resource files that are loaded at runtime via the QResource API, and not link the resource files directly to the application.

Currently the new target-based qt6_add_resources function does not allow doing that.

Investigate how we could do that.