fix: allow <p> inside of <hgroup> (#5338)

Ref webstudio-is/webstudio-community#241

Never supported heading outline algorithm was never supported and the
latest update to html spec allowed paragraphs as part of this removal
for lower level subtitles or descriptions.

Though indices tables were not updated. I [sent
PR](whatwg/html#11524)

Author: TrySound

packages/html-data/bin/elements.ts

@@ -76,6 +76,12 @@ const elementsByTag: Record<string, Element> = {};
       if (tag === "summary") {
         categories.push("interactive");
       }
+      // hgroup also accepts paragraphs
+      // https://html.spec.whatwg.org/multipage/sections.html#the-hgroup-element
+      // https://github.com/whatwg/html/pull/11524
+      if (tag === "hgroup") {
+        children.push("p");
+      }
       elementsByTag[tag] = {
         description,
         categories,