fix(compiler-sfc): fix template usage check edge case for v-on statements

ref: https://github.com/vuejs/vue/issues/12591

packages/compiler-sfc/src/compileScript.ts

@@ -2134,6 +2134,8 @@ function processExp(exp: string, dir?: string): string {
   if (/ as\s+\w|<.*>|:/.test(exp)) {
     if (dir === 'slot') {
       exp = `(${exp})=>{}`
+    } else if (dir === 'on') {
+      exp = `()=>{${exp}}`
     } else if (dir === 'for') {
       const inMatch = exp.match(forAliasRE)
       if (inMatch) {