Symbols: a symbol nested in symbol art is measured by its own art

Document::symbol_art_bounds measured a symbol's art without the
document, so an instance of another symbol in that art counted as the
20 x 20 square. It now measures the art through SymbolBoxes, so a nested
instance takes its own symbol's art, and an inline graphic of the outer
symbol is sized by it and follows it when that symbol changes.

- The inline resolve order also follows the instances that size a
  symbol's art, so a symbol is measured after the type in the art of
  the symbols it holds is laid out again.
- A symbol whose art reaches itself through an instance and an inline
  graphic is an empty slot. Only instances that the measurement uses
  count, so one a clipping path hides adds no dependency.
- A missing symbol, a symbol without art, a symbol that holds an
  instance of itself, and nesting 32 deep still measure as the square.
- SymbolBoxes finds symbols through a name index built once, and the
  inline resolve pass and inline_art_bounds share one index, instead
  of scanning the symbol list for each lookup.

docs/target-app-parity.md

@@ -1314,6 +1314,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
 - **Manual kerning in right-to-left text:** a manual kerning value on a Hebrew or Arabic character changes the space between it and the next character in reading order, the one drawn to its left, under Auto and Optical kerning. The character before it keeps its place, and the caret between the pair stays beside the next character. The side the space goes on is VectorCraft's own rule. Behavior reference: [Line and character spacing](https://web.archive.org/web/20260916050333/https://helpx.adobe.com/illustrator/using/line-character-spacing.html). Test: `rtl_manual_kerning_spaces_the_character_from_the_next_in_reading_order`.
 - **Manual kerning on inline graphics:** a manual kerning value on an inline graphic's character spaces it from the next character in reading order by the same distance as on a letter of its run's size, in left-to-right, right-to-left and vertical type; Auto and Optical kerning still apply no font pairs to it. This is VectorCraft's own rule. Test: `manual_kerning_on_an_inline_graphic_spaces_it_like_a_letter`.
 - **Inline graphics in symbol art follow their symbols:** when a symbol changes, type with an inline graphic of it is laid out again wherever the type is: in the layers, in the art of other symbols, graph designs and pattern tiles, and in opacity masks. A symbol's type is laid out before the type that shows that symbol inline, so a symbol whose art holds an inline graphic, its instances and the inline graphics that show it take its new size. Opening and reverting a document and Refresh Font List resolve them in the same order. An inline graphic of a symbol whose art shows that symbol inline, directly or through other symbols, is an empty slot. This is VectorCraft's own rule. Tests: `inline_graphics_in_symbol_art_follow_their_symbol`, `inline_graphics_in_masks_and_pattern_tiles_follow_their_symbol`, `symbols_are_resolved_after_the_symbols_they_show_inline`, `a_symbol_that_shows_itself_inline_is_an_empty_slot` in `crates/engine/src/tests/inline.rs`.
+- **Inline graphics of symbols that hold other symbols:** an inline graphic of a symbol whose art holds an instance of another symbol is sized by that symbol's own art, placed by the instance, and follows it when that symbol changes. A symbol's type is laid out after the type in the art of the symbols its instances show. An inline graphic of a symbol whose art reaches that symbol through an instance and an inline graphic is an empty slot; an instance that does not size the art, such as one a clipping path hides, does not count. An instance of a missing symbol, of a symbol without art, of a symbol that holds an instance of itself, or of a symbol whose art nests symbols 32 deep is measured by the 20 × 20 square. This is VectorCraft's own rule. Tests: `an_inline_graphic_follows_the_art_of_a_symbol_nested_in_its_symbol`, `symbols_are_resolved_after_the_symbols_their_instances_show`, `a_symbol_that_shows_itself_through_an_instance_is_an_empty_slot` in `crates/engine/src/tests/inline.rs`; `a_symbol_nested_in_symbol_art_is_measured_by_its_own_art`, `nested_instances_without_art_of_their_own_are_measured_by_the_square`, `only_instances_that_size_a_symbols_art_make_it_depend_on_their_symbol` in `crates/doc/src/inline.rs`.
 - **Recent font pickers (#3515):** The shared Character, Properties, Glyphs and Find Font family picker lists recently applied families first, once each, in most-recent order and limited by Preferences › Type › Number of Recent Fonts. Search and filters apply to both sections; unavailable families are omitted. Section headings cannot be selected or previewed. Confirmed character-range font edits update the same saved history; previews and failed edits do not. Requirement: [issue #3515](https://github.com/storytold/vectorcraft/issues/3515).
 - **Show samples on white (a VectorCraft addition):** Preferences › Type › Show samples on white (`fontSamplesOnWhite`, off by default) draws each family's sample in every font menu, and in Type → Font in the in-window menu bar, in dark type on a white area in every interface brightness. A highlighted row's color shows above and below the white area, and the names and the rest of the menu keep the interface's colors. The checkbox is dimmed while Enable in-menu font previews is off. Tests: `crates/ui-egui/src/tests/font_menu.rs`, `crates/ui-egui/src/font_menu/tests.rs`, `crates/ui-egui/src/prefs_dialog/tests.rs`.
 - **Find Font: Replace With Font From:** a dropdown under Replace With Font chooses the list the replacement font comes from: Document lists the families the document uses, once each; Recent lists the recently applied families that are installed (fonts applied with Find Font's Change and Change All included), newest first, as many as Preferences › Type › Number of Recent Fonts allows; System, the default, lists the installed families available in the font menu. The dialog opens on System with Source Sans 3 chosen, or the font menu's first family when Source Sans 3 is not installed. Choosing a list keeps the chosen font when the list has it and it is installed; otherwise Document and Recent choose the list's first installed font, and System chooses Source Sans 3 or the font menu's first family. Change and Change All are unavailable when the list has no installed font (Recent before any font was applied) and when the chosen family is not installed or is not in the shown list. Behavior reference: [Find and replace fonts](https://helpx.adobe.com/illustrator/desktop/design-with-text/fonts-and-scripts/find-and-replace-fonts.html) (public documentation). Tests: `crates/ui-egui/src/find_font.rs`.