new linkify handling

Should fix mentions in non-HTML messages

lib/helpers/extensions/linkify_html.dart

@@ -0,0 +1,45 @@
+import "package:html/dom.dart";
+import "package:html/parser.dart";
+import "package:linkify/linkify.dart";
+import "package:nexus/helpers/matrix_linkifier.dart";
+
+extension LinkifyHtml on String {
+  /// Wraps bare links in this HTML's text in `<a>` tags.
+  ///
+  /// Only text nodes are touched, so attribute values are left alone, and
+  /// text already inside a link or code is skipped.
+  String get linkifiedHtml {
+    final fragment = parseFragment(this);
+    _linkifyNode(fragment);
+    return fragment.outerHtml;
+  }
+}
+
+void _linkifyNode(Node node) {
+  if (node is Element && const {"a", "code", "pre"}.contains(node.localName)) {
+    return;
+  }
+
+  for (final child in node.nodes.toList()) {
+    if (child is! Text) {
+      _linkifyNode(child);
+      continue;
+    }
+
+    final elements = linkifyText(child.data);
+    if (!elements.any((element) => element is LinkableElement)) continue;
+
+    elements
+        .map(
+          (element) => switch (element) {
+            LinkableElement(:final text, :final url) =>
+              Element.tag("a")
+                ..attributes["href"] = url
+                ..append(Text(text)),
+            _ => Text(element.text),
+          },
+        )
+        .forEach((replacement) => node.insertBefore(replacement, child));
+    child.remove();
+  }
+}