fix: explicitly export ssrRegisterHelper as const in plugin-vue-jsx

Author: luckydye

packages/plugin-vue-jsx/src/index.ts

@@ -15,7 +15,7 @@ export * from './types'
 const ssrRegisterHelperId = '/__vue-jsx-ssr-register-helper'
 const ssrRegisterHelperCode =
   `import { useSSRContext } from "vue"\n` +
-  `export ${ssrRegisterHelper.toString()}`
+  `export const ssrRegisterHelper = ${ssrRegisterHelper.toString()}`
 
 /**
  * This function is serialized with toString() and evaluated as a virtual