Use plaintext value for field value tooltips in web UI (#7388)

Fix #7383

app/javascript/mastodon/utils/html.js

@@ -0,0 +1,6 @@
+export const unescapeHTML = (html) => {
+  const wrapper = document.createElement('div');
+  html = html.replace(/<br \/>|<br>|\n/g, ' ');
+  wrapper.innerHTML = html;
+  return wrapper.textContent;
+};