maps: mapboxgl plugin doesn't work in multiprocess mode with Qt from installer

[WARN | default | c.p.map] QOpenGLContext is NULL!
[WARN | default | c.p.map] You are running on QSG backend  "software"
[WARN | default | c.p.map] The MapboxGL plugin works with both Desktop and ES 2.0+ OpenGL versions.
[WARN | default | c.p.map] Verify that your Qt is built with OpenGL, and what kind of OpenGL.
[WARN | default | c.p.map] To force using a specific OpenGL version, check QSurfaceFormat::setRenderableType and QSurfaceFormat::setDefaultFormat