Implement better markdown escaping and inline code escape (#23222)

Motivation for this is using markdown for keymap error notifications in
#23113, but it also benefits the copied text of repl tables.

Release Notes:

- N/A

crates/util/src/util.rs

@@ -1,6 +1,7 @@
 pub mod arc_cow;
 pub mod command;
 pub mod fs;
+pub mod markdown;
 pub mod paths;
 pub mod serde;
 #[cfg(any(test, feature = "test-support"))]