Brushes: renaming or deleting a brush updates every stroke that uses it

Delete Brush and a rename in Brush Options changed only the strokes in
the layers. Strokes in symbol definitions, graph designs, pattern
tiles, opacity masks, graphic styles and the art of other brushes kept
the old brush name. After a rename they drew as plain strokes, and
after a delete a brush made later with the same name painted them.

brush.delete and brush.options with newName now rename the brush, or
clear it, in every stroke in those places, and in the tile that
pattern editing's Cancel puts back. Only the objects that change, and
the groups that hold them, are copied. It is still one undo step.

Docs: docs/target-app-parity.md.

docs/target-app-parity.md

@@ -722,6 +722,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
     In the Brushes panel, Shift-click selects a range of brushes and Ctrl/Cmd-click adds or removes one. Delete Brush and Duplicate Brush then act on all of them (`brush.delete {names}`, `brush.duplicate {names}`).
     Document Info has a Brushes category after Graphic Styles. It lists the Brushes panel's brushes, or with Selection Only it lists the brushes that the selected objects' strokes use. The Document Info report and Package's report list them too (`document.info {category: "brushes"}`, `brushNames`).
     The Brushes panel menu's Select All Unused selects the brushes that are not used in the document, as the [Brushes](https://web.archive.org/web/20241230205225/https://helpx.adobe.com/illustrator/using/brushes.html) page (archived copy) describes. A brush counts as used when a stroke paints with it in the art (opacity masks included), in symbols, graph designs, pattern tiles or graphic styles, or in the art of a used brush (`brush.unused`).
+    A rename in Brush Options and Delete Brush change every stroke that paints with the brush: in the layers and opacity masks, symbols, graph designs, pattern tiles, graphic styles and the art of other brushes. A rename gives those strokes the new name, and Delete Brush makes them plain strokes, in one undo step.
   - **Appearance:** the Appearance panel's selected row drives every paint, stroke, gradient and transparency edit (`item` on the commands); effects apply to one fill or stroke; per-item Opacity popups, whose blend-mode list and opacity slider stay open inside them (#430; the Control bar's Stroke popover too); Mixed Appearances, Layers target dots and basic-appearance rules. Effects can be reordered, moved between items and copied by dragging; Show All Hidden Attributes; clicking an effect edits it in place; the object thumbnail drags onto art; effects render on type, images, symbols, blends, envelopes, meshes and repeats, and per-item raster effects export. Groups, layers and type have their own fills, strokes and effects (Contents and Characters rows); the Layers panel's target circles target layers, groups and objects; Expand Appearance turns fills, strokes, effects and brushes into objects.
     Fill and stroke paint (Fill, Stroke, None, Apply Last Color and Apply Last Gradient, also on characters selected with the Type tool), the Stroke panel's options, gradient and freeform point edits, Swap Fill and Stroke, Default Fill and Stroke, the Eyedropper, and the Appearance panel's item edits, Clear Appearance, Reduce to Basic Appearance, Remove Item, item reordering and Move Appearance record no undo step when they change nothing.
     An image's own fills and strokes draw the shape that a Convert to Shape or Outline Object effect on them gives them (the image's box or its frame, reshaped by the effects after it), under or over the image as its Contents row says, on the canvas, in exports and through Expand Appearance; new fills and strokes on an image go under it. Without one of those effects they draw nothing, and Use Preview Bounds measures an image by its frame.