T21b and T21c: Documents, reading and knowledge

- DocumentViewer: pages the app drew on a desk, the page under the view's middle
  counted, zoom steps and fit, thumbnails, notes pinned where a press lands, and
  the owner's FindWidget over the pages, hits lit and the current one revealed
- PageThumbnailList, EpubReader (chapters, type size, progress), PrintPreview
- MarkdownRenderer feeds TableOfContents through sections and outline
- Footnote, TooltipTerm, Glossary, ReadingProgress, ZenMode
- Backlinks, Favorites, TrashBin, PageCover, PageIcon, TemplatePicker,
  VersionHistory with PageHistoryDiff
- editor::FindWidget shows the replace fold and option toggles only with handlers
- block editor tests move to documents/blocks
- icons: a-arrow-down, a-arrow-up
- gallery: reading and knowledge sections; scripted find, changes and zen

examples/gallery/pages/documents/mod.rs

@@ -1,4 +1,6 @@
 mod editing;
+mod knowledge;
+mod reading;
 
 use gpui::{AnyElement, App, IntoElement, ParentElement, Window, div};
 
@@ -58,8 +60,31 @@ const SCRIPT: &[Step] = &[
     Step::HoverAt("doc-blocks", 120.0, 20.0),
     Step::Wait(300),
     Step::Shot("handle"),
+    Step::DownAt("read-viewer", 440.0, 58.0),
+    Step::UpAt("read-viewer", 440.0, 58.0),
+    Step::Key("cmd-a"),
+    Step::Type("lift"),
+    Step::Wait(200),
+    Step::DownAt("read-viewer", 786.0, 58.0),
+    Step::UpAt("read-viewer", 786.0, 58.0),
+    Step::Wait(400),
+    Step::Shot("find"),
+    Step::DownAt("know-versions", 330.0, 22.0),
+    Step::UpAt("know-versions", 330.0, 22.0),
+    Step::Wait(300),
+    Step::Shot("changes"),
+    Step::DownAt("read-zen", 60.0, 24.0),
+    Step::UpAt("read-zen", 60.0, 24.0),
+    Step::Wait(500),
+    Step::Shot("zen"),
+    Step::Key("escape"),
+    Step::Wait(300),
 ];
 
 fn render(window: &mut Window, cx: &mut App) -> AnyElement {
-    div().child(editing::editing(window, cx)).into_any_element()
+    div()
+        .child(editing::editing(window, cx))
+        .child(reading::reading(window, cx))
+        .child(knowledge::knowledge(window, cx))
+        .into_any_element()
 }