Selection: Make SelectionManager weak-referenceable

[drowaudio]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 53.48%. Comparing base (2fcbe37) to head (33e5595).
⚠️ Report is 4 commits behind head on feature/v3_5.

Files with missing lines	Patch %	Lines
...tion_engine/selection/tracktion_SelectionManager.h	0.00%	1 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           feature/v3_5     #286      +/-   ##
================================================
- Coverage         53.49%   53.48%   -0.01%     
================================================
  Files               541      541              
  Lines             72525    72526       +1     
  Branches          11666    11668       +2     
================================================
- Hits              38794    38792       -2     
- Misses            33730    33733       +3     
  Partials              1        1              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.