Migrate Chrome extension to Manifest V3

[Pharb]

Notes:

• "suggested_key" auto-conversion of "Ctrl" to "Command" on Mac does not work as documented by MDN / Chromium (I suspect this is a bug in Chromium, workaround is simple enough)
• service worker does not follow current best practises regarding storage and timers (good enough for now, can be further improved)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (8e86e53) to head (e34cb50).

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #261   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            9         9           
  Lines          738       740    +2     
  Branches       135       137    +2     
=========================================
+ Hits           738       740    +2     

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