r21.1: no lineedits for magnetization in GUI sample editor

There is no lineedits to set magnetization in GUI sample editor.

Probably they were accidentally hidden along with external field editor.

Appeared in r21.0.

To be checked in main

changed milestone to %v21.1

added GUI release-critical labels

changed the description

mentioned in merge request !2021 (merged)

mentioned in commit 5fe6c1b6

closed with merge request !2021 (merged)