Support QML debugging in non-Qt/MSBuild *.vcxproj projects

A customer has an old, large *.vcxproj project that cannot be converted to Qt/MSBuild. They have a custom build command to run `rcc` to embed *.qrc resources into their executable.

They are able to manually set the QT_QML_DEBUG macro and pass the `qmljsdebugger` option to the debugged executable, but this is insufficient to provide a complete hook into the debugging infrastructure.

They would like a way to manually specify the location of QML sources to be mapped to the running executable.