Platform plugins can "lose" EGL version information

q_glFormatFromConfig (from qeglconvenience.cpp) does not set version, which means ES version will always be reported as 2. This has implications for e.g. Qt3D, when deciding to create an ES2 or ES3 helper. This impacts several of the platform plugins using q_glFormatFromConfig. The windows plugin seems to have been written to correctly handle this (http://code.qt.io/cgit/qt/qtbase.git/tree/src/plugins/platforms/windows/qwindowseglcontext.cpp#n339)