Add multi browser tests + wabac.js update (#420)

Fidelity: Fix CSP issue with iframes in Firefox (via wabac.js 2.23.0)
Loading: Avoid unnecessary reloads of multiWACZ JSON, prune expired
multiWACZ collections

Testing improvements:
- add playwright multi browser tests with firefox and webkit
- add test of iframe replay with iframetest.wacz

deps: update to wabac.js 2.23.0
bump to 2.3.9

tests/embed/index-sandbox.html

@@ -14,6 +14,7 @@
   </head>
   <body>
     <replay-web-page
+      noWebWorker
       embed="replay"
       src="http://localhost:9990/docs/examples/tweet-example.wacz"
       url="page:0"