Perf: Avoid creation of intermediary array when iterating over style rules (#1272)

* Perf: Avoid creation of intermediary array when iterating over stylesheet rules by using the second `mapFn` argument of Array.from

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/from

Performance analysis by: JonasBA <jonas@badalic.com>
Authored-by: Eoghan Murray <eoghan@getthere.ie>

packages/rrweb-snapshot/src/utils.ts

@@ -98,7 +98,7 @@ export function stringifyStylesheet(s: CSSStyleSheet): string | null {
     const rules = s.rules || s.cssRules;
     return rules
       ? fixBrowserCompatibilityIssuesInCSS(
-          Array.from(rules).map(stringifyRule).join(''),
+          Array.from(rules, stringifyRule).join(''),
         )
       : null;
   } catch (error) {