As a general fact, it is delicate or impossible to maintain consistently the _pos, _pos3d or _embedding attributes of graphs under modifications (eg vertex/edge addition/deletion). In order to keep modifications as fast as possible, we simplify the handling of these attributes by just adding a consistency check in get_pos and get_embedding (that could modify the attributes when necessary). We also remove the updating that were previously done in vertex/edge deletions.

Depends on #34021
Depends on #34042

CC: @dcoudert @tscrim

Component: graph theory

Author: Vincent Delecroix

Branch/Commit: 7dbe1af

Reviewer: David Coudert

Issue created by migration from https://trac.sagemath.org/ticket/33760