Fixes adding bookmarks and folders to the existing folders

[NejcZdovc]

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.)

Resolves #12478
Resolves #12477

Auditors:

Test Plan: defined in #12478 and #12477

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

[codecov-io]

Codecov Report

Merging #12500 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #12500   +/-   ##
=======================================
  Coverage   55.91%   55.91%           
=======================================
  Files         278      278           
  Lines       26975    26975           
  Branches     4363     4363           
=======================================
  Hits        15082    15082           
  Misses      11893    11893

Flag	Coverage Δ
#unittest	55.91% <100%> (ø)	⬆️

Impacted Files	Coverage Δ
app/common/cache/bookmarkOrderCache.js	99.07% <100%> (ø)	⬆️

[bsclifton]

++

[bsclifton]

master d550194
0.21.x 7c31f00
0.20.x 6c1ce49