gg: expose sapp_desc.swap_interval via gg.Config (#11975)

vlib/gg/gg.c.v

@@ -198,6 +198,7 @@ pub fn new_context(cfg Config) &Context {
 		enable_dragndrop: cfg.enable_dragndrop
 		max_dropped_files: cfg.max_dropped_files
 		max_dropped_file_path_length: cfg.max_dropped_file_path_length
+		swap_interval: cfg.swap_interval
 	}
 	g.window = window
 	return g

vlib/gg/gg.v

@@ -66,6 +66,7 @@ pub:
 	fullscreen    bool
 	scale         f32 = 1.0
 	sample_count  int
+	swap_interval int = 1 // 1 = 60fps, 2 = 30fps etc. The preferred swap interval (ignored on some platforms)
 	// ved needs this
 	// init_text bool
 	font_path             string