[Windows]: QWindowsEGLContext should use the void(*)() approach instead of the __eglMustCastToProperFunctionPointerType typedef

[Windows]: QWindowsEGLContext should use the

void(*)()

approach instead of the __eglMustCastToProperFunctionPointerType typedef. The reason being that not all OpenGL ES implementations actually have that typedef, so we should not rely on it existing.