Sheet metal: sheet.perforate, a perforation field exported to the flat pattern and DXF (#732) (#1041)

Adds sheet.perforate: round holes on a staggered or square grid over the flat sheet, kept clear of edges, cut-outs and bend zones. The holes go to the flat pattern, the DXF and the measured volume rather than the B-rep, so a panel can carry many thousands of them.

crates/engine/src/cmd/edit.rs

@@ -844,6 +844,7 @@ fn redefine(s: &mut Session, p: &Value) -> Result<Value> {
             spec.id,
             "sheet.flange"
                 | "sheet.hem"
+                | "sheet.perforate"
                 | "sheet.fold"
                 | "sheet.unfold"
                 | "sheet.refold"