qmlproject does not have an "other files" section

1. Open a qmlproject file.
2. Select "File->New" and add a General/Text File.
3. Error message appears: "Failed to add one or more files to project ..."

Similar things happen with GLSL vertex and fragment shaders (.vert and .frag extensions) in creator/mainline. Doing the same thing with a C++ project works fine - it adds the file to the "Other Files" section. Also works fine if a text or shader file is created when no project is open - only qmlproject has an issue.

The culprit seems to be the lack of "Other Files" support in the qmlproject format. Qt/3D in particular will be introducing lots of "other files" to QML for 3D model formats, shaders, texture cube map formats, and so on.