fix: a projected edge stays the edge that was picked when its body changes (#730)

A sketch's link to a projected edge now keeps the edge's persistent name and finds it by that name when the body changes, instead of taking whichever edge ends up nearest its point.

crates/doc/src/format.rs

@@ -85,6 +85,10 @@
 //!   edges of a solid or shelled body that become bends). A conversion without `bends` is the
 //!   plate conversion it always was and saves as before; 0.8.0 would drop the bend edges and
 //!   refuse the body as no plate.
+//!   A sketch's link to a projected edge can also keep the edge's persistent name (`edge_name`,
+//!   beside `face_name`) and is then found by it, wherever the edge went. A link without it is
+//!   the edge nearest its point, as it always was, and takes the name when its sketch is next
+//!   edited.
 //!   A fillet's `fit` can be `taper` (the radius follows the room along each edge it doesn't
 //!   fit). Fillets with `exact` or `reduce` save as before; 0.8.0 would refuse the unknown fit.