T21a: Documents, editing

- markdown read with pulldown-cmark: marks for live styling, blocks, links, words
- forms::Highlight gains weight, slant and strike; measure and paint share runs
- Inter Italic embedded, so emphasis reads slanted
- forms::mention's popup and keys become Suggestions, shared with the editors
- RichTextEditor with FixedFormatToolbar, the floating toolbar, LinkEditor,
  @ and : suggestions, WordCount and ReadingTime
- MarkdownEditor: visual (a pressed block opens as source), source, split
- BlockEditor: prose, lists, to-dos, quotes, callouts, toggles, code, math,
  diagrams the app draws, dividers, tables that grow and merge, pictures to
  resize and align, cards for video and pages, columns, synced text; slash menu,
  markdown shortcuts, handles that drag and open a menu, one undo for all
- TodoItem and Checklist
- icons: heading-1..3, workflow, merge
- gallery: the Documents page with scripted states

src/forms/glyphs.rs

@@ -338,7 +338,7 @@ impl RenderOnce for IconPicker {
 }
 
 /// Emoji whose name or shortcode holds `query`, a lowercase string; all for an empty one.
-fn emoji_found(query: &str) -> Vec<&'static emojis::Emoji> {
+pub(crate) fn emoji_found(query: &str) -> Vec<&'static emojis::Emoji> {
     emojis::iter()
         .filter(|emoji| {
             query.is_empty()