chore: combine render() and draw() in backend

src/backend_glfw_opengl3.zig

@@ -20,11 +20,8 @@ pub fn newFrame(width: f32, height: f32) void {
     zgui.newFrame();
 }
 
-pub fn render() void {
-    zgui.render();
-}
-
 pub fn draw() void {
+    zgui.render();
     ImGui_ImplOpenGL3_RenderDrawData(zgui.getDrawData());
 }