types(reactivity): make Ref _shallow type public

[yangmingshan]

This will help to use @vue/reactivity standalone. Current I have to use // @ts-expect-error in my custom watch.

https://github.com/vue-mini/vue-mini/blob/master/packages/wechat/src/watch.ts#L152

[posva]

you are not explaining why you need that...

[yangmingshan]

@posva I think I did, but never mind. I use @vue/reactivity to build my own watch, so I need _shallow type, check the link above (Vue Mini is library base on Vue 3 for mini program).

[posva]

You are only saying it I need it so I can omit a ts-expect-error in my own code but you should explain why accessing this internal property is necessary and why you can't do otherwise

[yangmingshan]

As I said I'm using @vue/reactivity to building my own watch, it's just like watch in Vue but without Vue special runtime binding. In this commit Evan use _shallow mark to determine whether a ref can be force trigger. I need to do same thing in my custom watch, use same _shallow mark, to fix same bug.

Hopefully I explained clearly why I need it, and why I can't do otherwise.

[yangmingshan]

@posva Can we move this PR forward?

[posva]

You still haven't explained with a proper use case what can't be done currently and requires the exposing of an internal variable to do so.

[yangmingshan]

Thinking in this way, @vue/reactivity is a library can be used standalone, I'm using it to build a mini fork Vue for real word use case in China. _shallow is internal for Vue not @vue/reactivity, it should be public for @vue/reactivity, because @vue/runtime-core is using it. And in my mini fork Vue's runtime-core need use it to solve #2231 just like Vue itself.

[yangmingshan]

@posva I appreciate your help, but I really try my best 😅, if you still don't get it, maybe we can ask another one to review this PR?