Add support for stable ids

[gosoares]

In my project, i have to provide the Itens ids to recycler view, and a did something like:

override fun getItemId(position: Int) : Long {
        val section = getSectionForAdapterPosition(position)
        val item = getPositionOfItemInSection(section, position)
        ...
        return id
}

With this update, it became simpler, because it already provides section and item indexes. Sorry if it have some grammar errors, i am still learning english.

[ShamylZakariya]

This looks like a good idea, but I'd like to see en example of it in use before adding more complexity.