new feature: support Vue CLI 5 can load both vue.config.js and vue.config.ts

[screetBloom]

I want to implement a pr that supports @vue/cli-service@5 to load both vue.config.js and vue.config.ts

Does anyone have an opposing or agreeing opinion? The effect will look like this 👇

I expect to finish it in this week

The advantage of this feature is that the configuration file in the TS project is also vue.config.ts
The DX will be better

@sodatea @fangbinwei

[haoqunjiang]

Cool!