revert: sidebar widget registry refactor

[arbrandes]

Description

This reverts two recent commits that refactored the sidebar to use a widget registry mechanism (PRs #1885 and #1897):

• Revert "feat: move discussion topic prefetch from trigger to widget config lifecycle (feat: move discussion topic prefetch from trigger to widget config lifecycle #1897)" (59113b0)
• Revert "feat: decouple notifications panel using widget registry mechanism (feat: decouple notifications panel using widget registry mechanism #1885)" (0664dc3)

This feature will have to be refactored with backward compatibility in mind.

[codecov]

Codecov Report

❌ Patch coverage is 93.47258% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.16%. Comparing base (59113b0) to head (cd38f6b).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...urseware/course/new-sidebar/common/SidebarBase.tsx	73.52%	9 Missing ⚠️
...ware/course/new-sidebar/SidebarContextProvider.tsx	90.90%	6 Missing ⚠️
...-notifications/DiscussionsNotificationsTrigger.tsx	91.66%	4 Missing ⚠️
...urseware/course/sidebar/SidebarContextProvider.jsx	86.95%	3 Missing ⚠️
...eware/course/sequence/lock-paywall/LockPaywall.jsx	81.81%	2 Missing ⚠️
...otifications/notifications/NotificationsWidget.tsx	95.23%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1898      +/-   ##
==========================================
- Coverage   91.28%   91.16%   -0.12%     
==========================================
  Files         343      349       +6     
  Lines        5770     5830      +60     
  Branches     1388     1348      -40     
==========================================
+ Hits         5267     5315      +48     
- Misses        484      498      +14     
+ Partials       19       17       -2     

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[arbrandes]

We ended up making the thing backward compatible instead.