android: Preferences DataStore 和 Proto DataStore use guide

replace SharedPreferences by DataStore<Preferences> with kotlin

in Datastore Doc, it provide two way to use DataStore<Preferences>,

user can use kotlin or java language to implement it. But in fact, use java to implement it will be very different.
Maybe you can use Rxjava to simplify it, but in fact, use Rxjava to implement it is also not easy.
use kotlin will very simple to implement it? yes. and it’s ONLY ONE WAY to use it by kotlin.

steps

1. init DataStore<Preferences> object:

   private val Context.dataStore: DataStore<Preferences> by preferencesDataStore(name = "settings")
   private val switchStateKey = booleanPreferencesKey("toggle")
   

2. get value from defined key:

       dataStore.data.map {
        
        
           it[switchStateKey]