Rename activation generation to scroll generation.

[mstange]

As requested in review comments in #4478.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (main@dc8b7cc). Click here to learn what that means.
Patch coverage: 100.00% of modified lines in pull request are covered.

❗ Current head 7a34102 differs from pull request most recent head 44d5eb3. Consider uploading reports for the commit 44d5eb3 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4481   +/-   ##
=======================================
  Coverage        ?   88.64%           
=======================================
  Files           ?      284           
  Lines           ?    25587           
  Branches        ?     6882           
=======================================
  Hits            ?    22681           
  Misses          ?     2701           
  Partials        ?      205           

Impacted Files	Coverage Δ
src/app-logic/url-handling.js	86.55% <ø> (ø)
src/components/app/BottomBox.js	42.42% <ø> (ø)
src/reducers/url-state.js	96.00% <100.00%> (ø)
src/selectors/url-state.js	98.56% <100.00%> (ø)

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[julienw]

lgtm, thanks