M3.31: Swatches panel menu adds used colours, selects unused, merges, ungroups and sorts by kind

New commands: swatch.addUsedColors {selection?, global?} adds a swatch for
each colour the art uses that no solid swatch has (optionally global, the
art linking to them); swatch.unused lists the swatches nothing uses (links,
colours, gradients and patterns in art, symbols, pattern tiles and graphic
styles count); swatch.merge keeps the first colour and relinks the others'
art; swatch.ungroup and swatch.sortByKind (process, spot, gradients,
patterns). Each edit is one undo step; the panel menu items are enabled.
Document::visit_paints walks every paint of a document.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/doc/src/swatches.rs

@@ -105,6 +105,23 @@ impl Document {
     }
 }
 
+impl Document {
+    /// Visit every paint held by the art, symbol definitions, pattern tiles and graphic styles
+    /// (fills, strokes and text runs), and the colour of every gradient-mesh point as a solid paint.
+    pub fn visit_paints(&self, f: &mut dyn FnMut(&Paint)) {
+        let mut tree = |n: &Node| {
+            n.walk(&mut |m| {
+                node_paints(m).for_each(&mut *f);
+                if let NodeKind::Mesh(mesh) = &m.kind {
+                    mesh.points.iter().for_each(|p| f(&Paint::solid(p.color)));
+                }
+            })
+        };
+        self.layers.iter().chain(self.symbols.iter().map(|s| &s.art)).chain(self.patterns.iter().flat_map(|p| &p.art)).for_each(|n| tree(n));
+        self.graphic_styles.iter().flat_map(|gs| &gs.appearance.items).for_each(|it| f(item_paint(it)));
+    }
+}
+
 /// The default name of a solid swatch: its values in its own colour model ("C=10 M=20 Y=30 K=0",
 /// "R=255 G=128 B=0", "Gray K=40").
 pub fn color_name(c: Color) -> String {