Add ability to turn off devtools on vuex by passing an off options

[Austio]

This PR adds the ability to turn off devtools on a per vuex instance level. This is useful for cases where you have multiple vuex stores on a single page. A good example is a scenario where teams maintain their own portions of a single app that are all loaded, some of which will have an independent vuex store.

With this option, on the dev side i could turn this off per instance so that I can debug a single store.

By default, this mirrors what is already in vuex, it just allows for turning off when specified.

const store = new Vuex.Store({
  devtools: false
})

Follow through on #875

[ktsn]

I guess it may be cleaner to use Vue.config.devtools as default value of options.devtools rather than conjunction of both. like:

const devtools = options.devtools !== undefined ? options.devtools : Vue.config.devtools

// ...

if (devtools) {
  // ...
}

[Austio]

I had thought about this approach as well. I ended up on this way because i think we want to respect someone turning it off in Vue, which acts more like a parent here.

I could see both side of it though, what do you think from that perspective?

[ktsn]

I see the point as well. But I personally still feel that the default value is better because of intuitiveness. I'm concerning that the user may be confused if Vue's devtools config overwrites Vuex's one when they are not sure about that behavior. I also don't come up with any use cases for the behavior. 🤔

[Austio]

Ah, so if someone has this set to true in dev but ships to prod. It would still attach to the vue devtools if VUE_DEVTOOLS_GLOBAL_HOOK exists (have saw this exist before when vue devtools are off.)

Going to switch around to your recommendation.

[Austio]

@ktsn updated ⬆️

[ktsn]

Thanks!