A11Y: Add heading role for post titles. (#13143)

Not all screen readers treat articles as navigable roles when moving between landmarks. To help with this, we use a `heading` role on the title, with an arbitrary depth of 2 chosen as to not conflict with the main `<h1/>`. Because ARIA roles are used, this change should be entirely non-visual.

While this introduces minor navigation challenges in posts where headers are included, the vast majority of posts don't, and as screen reader users, we're used to mixed headers in longer-form content.

app/assets/javascripts/discourse/app/widgets/post.js

@@ -247,6 +247,13 @@ function showReplyTab(attrs, siteSettings) {
 createWidget("post-meta-data", {
   tagName: "div.topic-meta-data",
 
+  buildAttributes() {
+    return {
+      role: "heading",
+      "aria-level": "2",
+    };
+  },
+
   settings: {
     displayPosterName: true,
   },