Fixes edit flow for bookmarks and 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 #12484

Auditors:

Test Plan:

1. Have a folder on Bookmarks Toolbar
2. Right click on the folder, Edit Folder
3. Change location to be 'Other Bookmarks' instead of 'Bookmarks Toolbar', click Done.
4. Folder continues to display on Bookmarks Toolbar.

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 #12589 into master will increase coverage by <.01%.
The diff coverage is 73.33%.

@@            Coverage Diff             @@
##           master   #12589      +/-   ##
==========================================
+ Coverage   56.05%   56.05%   +<.01%     
==========================================
  Files         278      278              
  Lines       27065    27075      +10     
  Branches     4381     4384       +3     
==========================================
+ Hits        15172    15178       +6     
- Misses      11893    11897       +4

Flag	Coverage Δ
#unittest	56.05% <73.33%> (ø)	⬆️

Impacted Files	Coverage Δ
app/browser/reducers/bookmarksReducer.js	96.96% <100%> (+0.04%)	⬆️
app/common/state/bookmarkFoldersState.js	100% <100%> (ø)	⬆️
app/browser/reducers/bookmarkFoldersReducer.js	96.8% <63.63%> (-3.21%)	⬇️

[LaurenWags]

Tested with steps from PR and original steps from logged issue.
Additional test done:
Have folder on Bookmark Toolbar.
Open Bookmarks Manager.
Right click on folder under Bookmarks Toolbar, select Edit Folder.
Update location to be Other Bookmarks, save.
Folder no longer displays on Bookmarks Toolbar and appropriately displays under Other Bookmarks.

[bsclifton]

Will this condition ever get hit (null/undefined being passed in)? The caller isn't checking for null/undefined before calling .isEmpty() on the param

[bsclifton]

++

[bsclifton]

master 986e10e
0.21.x 0a62a7e
0.20.x 999e451