Update MD051/link-fragments to use the same character classes as GitHub, encode unprintable characters from emojii.

lib/md051.js

@@ -18,10 +18,19 @@ const identifierRe = /(?:id|name)\s*=\s*['"]?([^'"\s>]+)/iu;
  */
 function convertHeadingToHTMLFragment(inline) {
   const inlineText = inline.children.map((token) => token.content).join("");
-  return "#" + inlineText
-    .toLowerCase()
-    .replace(/ /g, "-")
-    .replace(/[^-_a-z0-9]/g, "");
+  return "#" + encodeURIComponent(
+    inlineText
+      .toLowerCase()
+      // RegExp source with Ruby's \p{Word} expanded into its General Categories
+      // eslint-disable-next-line max-len
+      // https://github.com/gjtorikian/html-pipeline/blob/main/lib/html/pipeline/toc_filter.rb
+      // https://ruby-doc.org/core-3.0.2/Regexp.html
+      .replace(
+        /[^\p{Letter}\p{Mark}\p{Number}\p{Connector_Punctuation}\- ]/gu,
+        ""
+      )
+      .replace(/ /gu, "-")
+  );
 }
 
 module.exports = {