Fix Brave bookmark drag-and-drop

[diracdeltas]

fix #10936

Test Plan:

1. go to about:bookmarks, try dragging and dropping some bookmarks. it should work.
2. drag a tab to change its position. it should work.
3. try detaching and reattaching tabs

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.

Test Plan:

Reviewer Checklist:

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

[diracdeltas]

While testing this out, I found a separate DnD issue on master (haven't tested other branches):

1. show the bookmarks toolbar
2. try to re-order the bookmarks in the toolbar
3. this does not trigger a renderer update, so the bookmark order is still the same. however if you trigger a renderer update by bookmarking a new page, the order suddenly changes.

[NejcZdovc]

@diracdeltas this is a know issue and it will be fixed with #10325

[NejcZdovc]

tried dnd bookmarks and folders in bookmark manager, tried dnd tabs (reordering), tried detaching and reattaching tabs and everything is working correctly

[NejcZdovc]

master 10f2ebf
0.20.x 7f2117c
0.19.x 899e417