Design tab (form editor) doesn't work with MCU projects by default

Steps to reproduce:

1. Ensure Qt for MCUs is installed 
2. Create a new MCU project in Qt Creator
3. Select a MCU kit (desktop or real hardware) 
4. Open the main QML file in the designer tab (form editor)

Expected result

The GUI is displayed as expected in the form editor.

Actual result

The form editor displays an error message:

Notes

This can be "fixed" by assigning a "Qt version" to the MCU kit. The problem is that "regular" Qt is not included with Qt for MCUs and therefore most users are not able to install a compatible Qt version.

Qt for MCUs "ships" a reduced subset of Qt, and that might be usable to fix the problem. Ideally though, the form editor should only depend on metadata provided by Qt for MCUs.