Improve learn folder contents display

[rtibbles]

Summary

• Reverts the folder side panel to show the topic level contents of the folder, rather than the skip logic folders
• Adds a visual divider between the end of the contents of a subtopic, and resources at the top level of the current topic
• Rejigs content display so that topics and resources are now shown in the proper order in the topic, with each subtopic displayed in-line, and then contiguous sequences of resources displayed together

References

Fixes #9043
Fixes #10060

Reviewer guidance

Look at large topics, small topics, deeply nested topics, topics that have resources and topics interspersed.

Good channels to look at: Kolibri QA channel, the HTML5 topic, Ciencia NASA channel - the Ciencia Espacial
topic.

Folder side panel:

Before	After

Resources in a topic after a subtopic now have a divider:

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Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

PR process

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.17.3a0.dev0_git.27.gf598d691.pex
Windows Installer (EXE)	kolibri-0.17.3a0.dev0+git.27.gf598d691-windows-setup-unsigned.exe
Debian Package	kolibri_0.17.3a0.dev0+git.27.gf598d691-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.17.3a0.dev0+git.27.gf598d691.dmg
Android Package (APK)	kolibri-0.17.3a0.dev0+git.27.gf598d691-0.1.4-debug.apk
TAR file	kolibri-0.17.3a0.dev0+git.27.gf598d691.tar.gz
WHL file	kolibri-0.17.3a0.dev0+git.27.gf598d691-py2.py3-none-any.whl

[pcenov]

Hi @rtibbles I confirm that this is implemented as specified, no issues observed while manually testing!

[marcellamaki]

At this point I only have questions, I'm not requesting specific changes, although depending on teh answers and how much I'm understanding (or not), I might have some suggestions about tweaks/additions to the code comments for some of the logic.

[marcellamaki]

With QA team approval and questions answered, this is good to merge. I do think it's a little bit dense with an array of either an array or objects, but I also think the solution is a good approach. ✅