Don't prefer STIXGeneral over the default font (#9711)

* Don't prefer STIXGeneral over the default font

STIXGeneral contains some glyphs for non-LGC scripts, but often doesn't implement these scripts fully. We should always try the browser's default fonts, which are likely to look nicer and have broader script support, before falling back to STIXGeneral.

* Explain why STIXGeneral shouldn't have precedence

* Add a regression test

cypress/e2e/polls/polls.spec.ts

@@ -115,7 +115,10 @@ describe("Polls", () => {
 
         const pollParams = {
             title: "Does the polls feature work?",
-            options: ["Yes", "No", "Maybe"],
+            // Since we're going to take a screenshot anyways, we include some
+            // non-ASCII characters here to stress test the app's font config
+            // while we're at it.
+            options: ["Yes", "Noo⃐o⃑o⃩o⃪o⃫o⃬o⃭o⃮o⃯", "のらねこ Maybe?"],
         };
         createPoll(pollParams);