Gmail-like CAB and "select items" logic

**Is your feature request related to a problem? Please describe.**
Not quite: it's something I would like to implement in my app.

**Describe the solution you'd like**
Please refer to the video below.

https://user-images.githubusercontent.com/56068232/188570449-05662635-1b48-457b-810f-dab4de538dfd.mp4

I would like to have a Gmail-like CAB (Contextual Action Bar) that shows up whenever the user enters the "select mode". This mode is triggered when there are no selected items and the user long presses one of the items in a list (in this case, emails). The new CAB should be different from the one that is shown when in "normal mode" (in this case, the CAB is absent when in "normal mode", and slides down without shifting the mails).

**Describe alternatives you've considered**
I've been toying around a little in [this snack](https://snack.expo.dev/@mbuffo/a925da), but I'm not happy with the result, especially with the "Hide appbar" transition.

**Additional context**
The video above should be enough.

Inizia esaminando il video collegato e l’Expo Snack di riferimento per comprendere le transizioni richieste di select-mode e CAB. Confronta quindi questo comportamento con l’app bar esistente di React Native Paper e i punti di ingresso della selezione; il lavoro è completato quando, durante una selezione con pressione prolungata, appare una CAB simile a quella di Gmail senza spostare l’elenco e distinta dalla modalità normale.

Scritto dal modello di indicizzazione a partire dal testo della issue.