documents: inline formats toggle as Typora's

MarkdownDocument::format toggles bold, italic, code, strike, underline,
link and image at the selection, or clears every inline mark from the
blocks it touches, following Typora's toggleStyle: off inside the style,
wrap a selection, take the caret's word or write an empty pair. Code,
math, HTML and front matter refuse, as does a selection crossing a
block, a link or another mark. An open block keeps its field open.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/documents/document/mod.rs

@@ -1,6 +1,7 @@
 mod attach;
 mod edit;
 mod finding;
+mod format;
 mod lists;
 mod look;
 mod parse;
@@ -22,6 +23,7 @@ use gpui::{
 
 pub use crate::documents::tree::DocumentHeading;
 pub use attach::Attachment;
+pub use format::{FormatRefusal, InlineFormat};
 pub use look::DocumentLook;
 use parse::{Parsed, alike, parsed};
 pub use point::{DocumentTarget, TargetBlock};