Handle unreliable timeouts/intervals

Background / User story

Manifest v3 forces us to run our background scripts in a service worker, which can be suspended/terminated at any time. Therefore we need to make sure that we can handle unreliable timeouts and intervals.

Note that the browser.alarms.* API that is meant to be used for those cases may not be reliable enough for all use cases:

• https://bugs.chromium.org/p/chromium/issues/detail?id=471524
• https://bugs.chromium.org/p/chromium/issues/detail?id=1245934

Potential breakage:

• Ongoing icon animation doesn't finish.
• Local first-run page doesn't open after remote first-run page fails to open.
• Local first-run page opens after remote first-run page was opened.
• Icon text doesn't update when blocked counter is incremented.
• Day-1 notification isn't shown.
• Total blocked counter isn't saved persistently.

What to change

• Design: TBD
• Research: TBD
• Spec: TBD
• Legal: TBD
• Development:
  • Use browser.alarms.* API in the background page instead of window.setInterval() and window.setTimeout().
    • Intervals
      • lib/devenvPoller: doPoll() (functionality can be removed altogether)
      • lib/icon: animateIcon() (see #1190)
    • Timeouts
      • lib/filterComposer: doInit() (only applies to Firefox)
      • lib/init
        • listenForRemotePage()
        • wait() (inconsequential and not possible due to closure)
      • lib/notifications: initDay1Notification()
      • lib/prefs: customSave.set("blocked_total") (only applies to Firefox <66)
      • lib/stats: scheduleBadgeUpdate()
  • Do not use browser.alarms.* API for intervals/timeouts that are less than 60s (see comment).

Hints for testers

See list of potential breakage under "Background".

Hints for translators

N/A