Feature request: Extend `mapper` to allow mapping to different names

[omnichronous]

Great feature, but can this be extend to allow us to rename the props names? Like vuex does with mapGetters, etc ?

Originally posted by @MateiNenciu in https://github.com/danielroe/typed-vuex/issues/264#issuecomment-1060700804

It would be awesome to have this, basically as described in the Vuex docs:

...mapGetters({
  // map `this.doneCount` to `this.$store.getters.doneTodosCount`
  doneCount: 'doneTodosCount'
})