[Glitch] Use plaintext value for field value tooltips in web UI

Port d185f3ddaf to glitch-soc

This doesn't change anything for glitch-style fields, but those will go
away eventually

app/javascript/flavours/glitch/util/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;
+};