feat(hero): 新增英雄按等级切换不同颜色描边的功能

新增紫色描边shader与对应材质资源，为英雄预制体注册四种颜色描边材质
重构FlashSprite组件支持按等级切换描边，在英雄初始化与升级时自动更新描边样式

assets/resources/game/gui/materials/outline-pur.mtl

@@ -0,0 +1,41 @@
+{
+  "__type__": "cc.Material",
+  "_name": "",
+  "_objFlags": 0,
+  "__editorExtras__": {},
+  "_native": "",
+  "_effectAsset": {
+    "__uuid__": "22f6acfb-c03d-4213-918a-4d3b0cce76b4",
+    "__expectedType__": "cc.EffectAsset"
+  },
+  "_techIdx": 0,
+  "_defines": [
+    {
+      "USE_TEXTURE": true
+    }
+  ],
+  "_states": [
+    {
+      "rasterizerState": {},
+      "depthStencilState": {},
+      "blendState": {
+        "targets": [
+          {}
+        ]
+      }
+    }
+  ],
+  "_props": [
+    {
+      "glowColor": {
+        "__type__": "cc.Color",
+        "r": 130,
+        "g": 46,
+        "b": 255,
+        "a": 255
+      },
+      "glowWidth": 0.002,
+      "glowThreshold": 0.887
+    }
+  ]
+}