Recolor: recolor.apply with a color group keeps art linked to the group's global swatches

Art linked to a global swatch of the group that recolor.apply rewrites stays
linked when the swatch takes its row's new color: it shows that color at its
tint, and a later swatch.edit still reaches it. Before, the art took the new
color unlinked. With group, the reply adds relinked, the count of other linked
paints that followed the group's new colors.

crates/engine/src/cmd/swatch.rs

@@ -830,6 +830,11 @@ impl GroupEdit {
     pub(super) fn defaults(&self, s: &mut Session) {
         self.relinks.iter().for_each(|r| r.defaults(s));
     }
+
+    /// How many paints linked to the group's swatches the rewrite changed.
+    pub(super) fn relinked(&self) -> usize {
+        self.relinked
+    }
 }
 
 /// Rewrite colour group `group` with `colors`: its swatches take them in order (keeping their