Watchers should be a core concept of Vuex

[lwxbr]

What problem does this feature solve?

This will make the flow of vuex, that is already very intuitive, more easier.

What does the proposed API look like?

In the analogy of component vs vuex:

data => state,
methods => mutations and actions ,
computed properties => getters,
watchers => watchers

The users will not have to use store.$watch, they will create watchers in the Vuex.Store and in modules directly.

The good news is that it will not destroy any existant flow, will only increase a feature that will help the flow of vuex.

This is the model of a module of vuex with watchers:

const state = {};
const getters = {};
const mutations = {};
const actions = {};
const watchers = {};

export default {
    namespaced: true,
	state,
	getters,
	mutations,
	actions,
	watchers,
}

[ktsn]

Duplicate of #1219