This adds window hints for the initial position, in screen coordinates,
of a window. The special value GLFW_ANY_POSITION means the window
manager will be allowed to position the window.
It is not possible to set window positions on Wayland and GLFW will
always behave as if these hints are set to GLFW_ANY_POSITION.
Fixes#1603Fixes#1747
This updates to a newer version of glad2 and switches to the header-only
variant.
This also (finally) switches to the newer glad2 loader signature that
allows us to pass in glfwGetInstanceProcAddress directly.