Add glfw.GetCocoaWindow

vendor/glfw/native_darwin.odin

@@ -0,0 +1,16 @@
+//+build darwin
+
+package glfw
+
+import NS "vendor:darwin/foundation"
+
+foreign import glfw { "lib/darwin/libglfw3.a" }
+
+@(default_calling_convention="c", link_prefix="glfw")
+foreign glfw {
+    GetCocoaWindow :: proc(window: WindowHandle) -> ^NS.Window ---
+}
+
+// TODO:
+// CGDirectDisplayID glfwGetCocoaMonitor(GLFWmonitor* monitor);
+// id glfwGetNSGLContext(GLFWwindow* window);