BREAKING: Defer creation of offscreen document in OffscreenExecutionService

[Mrtenz]

Previously, the offscreen document needed to be created from the OffscreenExecutionService because the extension did not do any offscreen set up. Nowadays though, the offscreen document is used by the extension for functionality other than Snaps, and the set up is handled from the extension.

Instead, we the offscreen service now accepts a Promise which should resolve when the offscreen document is ready. The service will wait for the promise to resolve before continuing.

[FrederikBolding]

@Mrtenz Can you update the PR title and description for the new content? Also should probably be marked as breaking

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.34%. Comparing base (caf42e3) to head (807deb6).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2473      +/-   ##
==========================================
- Coverage   94.34%   94.34%   -0.01%     
==========================================
  Files         439      439              
  Lines        9057     9054       -3     
  Branches     1392     1391       -1     
==========================================
- Hits         8545     8542       -3     
  Misses        512      512              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.