Fix view learn device regression

[ozer550]

Summary

• Only show "View learner devices" link when a learner with LOD setup actually exists.
• Only show learners that are using devices with LOD in ClassLearnersListPage.

lod-link-fix.mp4

References

closes #12947

Reviewer guidance

• Create a facility, users, and class where there is a coach and learner(s) but the learners are NOT on LODs
• Go to the exams page
  Observe that in the main exam page, and when clicking into a specific exam, see that the "View learner devices" link (and link to that page) is absent.
• Not setup the learner on LOD. Observe that "View learner devices" link is present and only shows the learners which are present on the lod.

[nucleogenesis]

I tested things out locally and things worked as expected. Overall, the code changes LGTM so once the tests are fixed up should be good to go.

[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.18.0b1.dev0_git.8.ga47b7a86.pex
Windows Installer (EXE)	kolibri-0.18.0b1.dev0+git.8.ga47b7a86-windows-setup-unsigned.exe
Debian Package	kolibri_0.18.0b1.dev0+git.8.ga47b7a86-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.18.0b1.dev0+git.8.ga47b7a86.dmg
Android Package (APK)	kolibri-0.18.0b1.dev0+git.8.ga47b7a86-0.1.4-debug.apk
Raspberry Pi Image	kolibri-pi-image-0.18.0b1.dev0+git.8.ga47b7a86.zip
TAR file	kolibri-0.18.0b1.dev0+git.8.ga47b7a86.tar.gz
WHL file	kolibri-0.18.0b1.dev0+git.8.ga47b7a86-py2.py3-none-any.whl

[ozer550]

I tested things out locally and things worked as expected. Overall, the code changes LGTM so once the tests are fixed up should be good to go.

Done!

[marcellamaki]

Hi @ozer550 - I think you're on the right track here, but there are a few adjustments needed to stay fully in line with the original intention of the issue/fix. I know some of the different learner setups can be complicated, so let me know if you want to discuss the scenarios more! I think it might make more sense once you can fully wrap your mind around picturing what this could look like in a classroom

[marcellamaki]

Thank you for the updates, @ozer550. This looks good and manual QA confirms it is working now as expected. Can you rebase, and then we can merge?(Let's use a squash merge for this :) )

[rtibbles]

We should be a little careful with this, as VueJS < 3 does not support reactive updates of ES6 Set objects: vuejs/vue#2410

I think in this case, the fact that we're always replacing the entire object is probably sufficient for this to retrigger a reactive update in the computed prop, but please be cautious in general with using Set and Map. This is the reason that we often just us a plain JS object when a Set or a Map might be more performant/semantic.