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.
This removes all dependencies from the GLFW test programs on the Vulkan
SDK.
It also removes support for linking the GLFW shared library (dynamic
library, DLL) against the Vulkan loader static library.
This adds the GLFW_SCALE_TO_MONITOR window hint for automatically
resizing the content area of a window to the requested size times the
monitor content scale each time it is placed on a new monitor. This
only applies to windowed mode windows and includes the initial placement
at window creation.
This hint only has an effect on platforms where screen coordinates and
pixels always map 1:1 such as Windows and X11. Platforms like macOS
instead change the resolution of the framebuffer independently of the
window size.
Related to #676.
Related to #1115.
