Developer manual: Section on typing annotations

<div id="comment:0"></div>

(from #32058)


CC:  @tobiasdiez @fchapoton @tscrim @egourgoulhon

Component: **documentation**

Author: **Matthias Koeppe**

Branch/Commit: **[`8f50198`](https://github.com/sagemath/sagetrac-mirror/commit/8f50198acd8e61328c928a4559d5d73d6382bf75)**

Reviewer: **Tobias Diez**

_Issue created by migration from https://trac.sagemath.org/ticket/32067_

