Event Aggregator Deadlock Fix

[JR-Morgan]

I was seeing a deadlock scenario in Rhino.

One thread was locking _subscriptions while publishing events, however in the callback of that event, it was trying to re-subscribe to an event, which was trying to re-enter a lock.

This PR replaces a yield enumerable with a list return to ensure that we aren't inside a lock during the executing of publish events.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 18.60%. Comparing base (4ee48bd) to head (718b88c).
Report is 1 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #568      +/-   ##
==========================================
+ Coverage   18.58%   18.60%   +0.01%     
==========================================
  Files         241      241              
  Lines        4939     4940       +1     
  Branches      586      586              
==========================================
+ Hits          918      919       +1     
  Misses       3990     3990              
  Partials       31       31              

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