Split scroll between titles and folders for BM manager

[cezaraugusto]

Test Plan:

• Have a lot of bookmarks
• Go to about:bookmarks
• Ensure that:
  • Layout is fixed
  • You can scroll between folders (left-hand side column) and titles (right-hand side column) wouldn't scroll together
  • Less-than-screen-height number of bookmakrs shouldn't let you scroll (layout is fixed)
  • At small sizes we fallback to what we have and you can scroll gracefully

Description

• 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).

• Auditors: @bsclifton

• Close Folders and Titles lists in about:bookmarks should scroll independently #5076

[cezaraugusto]

/cc @bradleyrichter for design review. Scrollbar is the same used for #8475

[jonathansampson]

Can we prevent the Title and Last Visited headers from scrolling with the content? Also, thoughts on adding an overflow-ellipsis to the title entries?

[cezaraugusto]

@jonathansampson yep that's the ideal but I can't since it uses <table> (SortableTable component) which doesn't accept overflow.

Ideally sortableTable should make use of css-grid to keep it's table-like look, but changes would be too bulk and imo deserves a standalone refactor.

++ for ellipsis. I'll do another round on this since Brad don't want custom sidebars and include that, thanks!

[jonathansampson]

@cezaraugusto All valid points. I gladly approve, provided we can create an issue to refactor the bookmarks items portion for frozen headers.

[bradleyrichter]

This is great to have, even with the unresolved header.

[cezaraugusto]

ok based on #8532 (comment) I created an issue to track fixed header for bm items: #8607. Also added ellipsis for long texts.

I also removed completely ScrollableContent element since component was created to address #7930 and this issue, and is no longer required.

[bsclifton]

Huge ++ on this 😄 Looks and feels awesome

This functionality was originally there but it was lost when I refactored the page into its current state