重构Legend图例，改变样式，增加自定义图标等设置

Assets/XChartsDemo/Runtime/Demo.cs

@@ -67,6 +67,18 @@ namespace XChartsDemo
             InitModuleButton();
         }
 
+        void ResetParam()
+        {
+            var charts = transform.GetComponentsInChildren<BaseChart>();
+            foreach (var chart in charts)
+            {
+                chart.themeInfo.defaultLegendTextColor = ThemeInfo.GetColor("#514D4D");
+                chart.legend.itemWidth = 20f;
+                chart.legend.itemHeight = 10f;
+                chart.legend.textStyle.fontSize = 16;
+            }
+        }
+
         void Update()
         {
 #if UNITY_EDITOR