Properly handle bookmarks/history session migration (w/ regard to split sites)

[bsclifton]

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed. (Ask a Brave employee to help if you cannot access this document.)

Fixes #10595

Automated test Plan:

npm run unittest -- --grep="sessionStore unit tests"

Manual test plan

1. Use Brave 0.19.x and ensure you have a decent number of:

• Bookmarks
• Bookmark folders (ex: enable bookmarks toolbar, move items around)
• History entries
• Pinned tabs

2. Install 0.20.x and launch into the same profile folder used for step 1 (because 0.20.x builds are beta, they use a different profile directory. You can launch using the --user-data-dir-name= param to ensure it uses the same profile

3. Verify you're on 0.20.x and that everything is present

• Bookmarks
• Bookmark folders
• History entries
• Pinned tabs

Reviewer Checklist:

• Request a security/privacy review as needed if one was not already requested.

Tests

• Adequate test coverage exists to prevent regressions
• Tests should be independent and work correctly when run individually or as a suite ref
• New files have MPL2 license header

[bsclifton]

PR is broken into two commits because 7caf16a was originally done back in September and does live in 0.21.x and 0.20.x, but for some reason is not in master

[codecov-io]

Codecov Report

Merging #12369 into master will increase coverage by 1.07%.
The diff coverage is 95.89%.

@@            Coverage Diff             @@
##           master   #12369      +/-   ##
==========================================
+ Coverage   55.34%   56.41%   +1.07%     
==========================================
  Files         276      277       +1     
  Lines       26758    27563     +805     
  Branches     4315     4749     +434     
==========================================
+ Hits        14808    15551     +743     
- Misses      11950    12012      +62

Flag	Coverage Δ
#unittest	56.41% <95.89%> (+1.07%)	⬆️

Impacted Files	Coverage Δ
app/sessionStore.js	86.76% <95.89%> (+11.56%)	⬆️
app/common/constants/settingsEnums.js	100% <0%> (ø)	⬆️
app/browser/activeTabHistory.js	90.32% <0%> (ø)
app/browser/reducers/autoplayReducer.js	98.93% <0%> (+1.63%)	⬆️
js/about/preferences.js	47.01% <0%> (+2%)	⬆️
app/common/lib/historyUtil.js	74.73% <0%> (+2.1%)	⬆️
app/browser/reducers/tabsReducer.js	45.75% <0%> (+2.23%)	⬆️
app/browser/api/ledgerNotifications.js	76.95% <0%> (+2.39%)	⬆️
...r/components/common/contextMenu/contextMenuItem.js	56.28% <0%> (+2.48%)	⬆️
... and 5 more

[NejcZdovc]

++ looks good to me, really nice job on the tests ❤️

[NejcZdovc]

master 5ccbfd2
0.21 16f13f1
0.20 5bfd06d