fix: update window export syntax for plugin; ensure compatibility with global scope

feat: add example usage for artplayer-plugin-test in test.js

docs/assets/example/test.js

@@ -0,0 +1,12 @@
+// npm i artplayer-plugin-test
+// import artplayerPluginTest from 'artplayer-plugin-test';
+
+var art = new Artplayer({
+    container: '.artplayer-app',
+    url: '/assets/sample/video.mp4',
+    plugins: [
+        artplayerPluginTest({
+            //
+        }),
+    ],
+});

scripts/plugin/template/src/index.js

@@ -27,5 +27,5 @@ if (typeof document !== 'undefined') {
 }
 
 if (typeof window !== 'undefined') {
-    window['{{export}}'] = {{export}};
+    window.{{export}} = {{export}};
 }