Dimension tool: Expand keeps a dimension as plain art after it moves

Object > Expand left a dimension's recipe on its group, so the next move
redrew the live dimension and discarded the expanded art. Expand now ends
the live link of a dimension whose art it changes, in the same undo step.
Moving or scaling the group leaves its art as it is, the art no longer
follows what it measured, and undo gives the live dimension back.

Expand Appearance, Create Outlines and Outline Stroke had the same fault
and now do the same, also when they reach only a part of a dimension. A
dimension whose art a command leaves as it was stays live. A dimension
selected with the art it measures becomes a plain group when Expand,
Expand Appearance or Outline Stroke replaces only that art.

docs/dimensions.md

@@ -36,8 +36,14 @@ changes); moved together with its art, it keeps its distance.
 
 Native `.vectorcraft` files keep the recipes and links. SVG, PDF and bitmap output contain
 ordinary paths and text, so exported dimensions look the same. Ungrouping a dimension leaves its
-paths and text as ordinary art. Pasted dimensions keep their geometry and drop their links, so
-they never bind to unrelated art in another document.
+paths and text as ordinary art. Object › Expand, Object › Expand Appearance, Type › Create Outlines
+and Object › Path › Outline Stroke turn a dimension whose art they change into a plain group of that
+art, also when they reach only a part of it: moving or scaling the group does not redraw it, it does
+not follow the art it measured, and undoing the command gives the live dimension back. A dimension
+selected with the art it measures also becomes a plain group when Object › Expand, Object › Expand
+Appearance or Object › Path › Outline Stroke replaces only that art. Pasted
+dimensions keep their geometry and drop their links, so they never bind to unrelated art in another
+document.
 
 ## Commands