Dimensional constraints: dynamic dimension persistence, lock mark, display variables, DIMCONSTRAINT

The dynamic dimension of a dimensional constraint is now linked in the
drawing file (AcDbAssocDependency + AcDbAssocDimDependencyBody on the
constraint node), reread on load, hidden by DCHIDE/DYNCONSTRAINTDISPLAY
and never plotted; it carries a lock mark before its text. New
CONSTRAINTNAMEFORMAT and DYNCONSTRAINTDISPLAY variables and the
DIMCONSTRAINT option front end. A transformed entity whose own end points
a driving dimension measures keeps only the first constraint point, so a
scaled line returns to its dimension value.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/scene/entity.rs

@@ -1402,6 +1402,9 @@ impl Scene {
                 }
                 if self.object_isolation.hides(common.handle)
                     || (!include_preview_hidden && self.preview_hidden.contains(&common.handle))
+                    || self.hidden_dynamic_dimensions.contains(&common.handle)
+                    // A dynamic dimension never plots.
+                    || (plot_only && self.is_dynamic_dimension(common.handle))
                 {
                     return false;
                 }