EGL: Replace native handle macros with functions

This change is in preparation both for EGL_EXT_platform_base and runtime
GLFW platform selection.

Related to #1691.

src/win32_window.c

@@ -2186,6 +2186,16 @@ const char* _glfwPlatformGetClipboardString(void)
     return _glfw.win32.clipboardString;
 }
 
+EGLNativeDisplayType _glfwPlatformGetEGLNativeDisplay(void)
+{
+    return EGL_DEFAULT_DISPLAY;
+}
+
+EGLNativeWindowType _glfwPlatformGetEGLNativeWindow(_GLFWwindow* window)
+{
+    return window->win32.handle;
+}
+
 void _glfwPlatformGetRequiredInstanceExtensions(char** extensions)
 {
     if (!_glfw.vk.KHR_surface || !_glfw.vk.KHR_win32_surface)