extension: Register navigator polyfill script with allFrames: true

This causes the browser to inject our polyfill script into iframes
as well as the main document. This ensures that we can always inject
the fake 'Shockwave Flash' plugin before the page's javascript has
a change to check 'navigator.plugins'

This fixes an inconsistent 'Flash Player Missing' error on
7Road Wartune

web/packages/extension/src/background.ts

@@ -189,6 +189,7 @@ async function enable() {
                     "https://*.edgenuity.com/*",
                 ],
                 runAt: "document_start",
+                allFrames: true,
                 world: "MAIN",
             },
             {