feat: implement a migrator that removes vue-next as it's no longer needed (#5725)

Author: haoqunjiang

packages/@vue/cli-service/migrator/index.js

@@ -0,0 +1,14 @@
+module.exports = (api) => {
+  if (api.hasPlugin('vue-next')) {
+    api.extendPackage({
+      devDependencies: {
+        'vue-cli-plugin-vue-next': null
+      }
+    },
+    {
+      prune: true
+    })
+
+    api.exitLog('vue-cli-plugin-vue-next is removed because Vue 3 support has been built into the core plugins.')
+  }
+}