Nested bookmark folder items should scroll and not the entire root folders

[srirambv]

• Did you search for similar issues before submitting this one?
  Yes

• Describe the issue you encountered:
  While testing Follow up to #7240, Bookmark import reduces performance when trying to open bookmarks from bookmark toolbar #9651, found that scrolling through bookmark items in nested folder, root folder go out of view (see screenshot)

• Platform (Win7, 8, 10? macOS? Linux distro?):
  Windows 10 x64

• Brave Version (revision SHA):

Brave	0.19.1
rev	2ee7a49
Muon	4.4.4

• Steps to reproduce:

  1. Clean install 0.19.1
  2. Import >5k bookmark
  3. Scroll through bookmarks in nested folders
  4. Root folders are not shown

• Actual result:
  See screenshot

• Expected result:
  Root folders should remain in focus only nested bookmark folder contents should scroll

• Will the steps above reproduce in a fresh profile? If not what other info can be added?
  Yes

• Is this an issue in the currently released version?
  May be need to verify, could be an existing issue

• Can this issue be consistently reproduced?
  Yes

• Extra QA steps:
  1.
  2.
  3.

• Screenshot if needed:
  

• Any related issues: