[MCU] Default Controls font in preview is different than with the real QUL backend

Steps to reproduce:

1. Create a MCU project in QDS
2. Add the Qt Quick Controls module to the main QML file
3. Add some Controls to the form, e.g., Button, or Checkbox
4. Start the Live Preview from Qt Design Studio
5. Build and run the same application with Qt for MCUs from Qt Creator

Expected result:

The two applications look identical. The default fonts used in QDS live preview match the ones used by QUL.

Actual result:

The default font family and size is different in QDS preview.

Notes:

• The same problem can be observed in QDS form editor