top level exception handler give a better exception when toasts fail

[JR-Morgan]

When Top level exception toasts fail to display, the exception message is lost

Here, I've adjusted the top level exception handler behaviour to handle toast faliures with an aggregate exception, and provide a better exception message when this occurs.

[codecov]

Codecov Report

Attention: Patch coverage is 73.33333% with 4 lines in your changes missing coverage. Please review.

Project coverage is 9.36%. Comparing base (d0e77d2) to head (e1e45ac).
Report is 1 commits behind head on dev.

Files with missing lines	Patch %	Lines
....Connectors.DUI/Bridge/TopLevelExceptionHandler.cs	73.33%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             dev    #423      +/-   ##
========================================
+ Coverage   9.30%   9.36%   +0.05%     
========================================
  Files        224     224              
  Lines       4234    4241       +7     
  Branches     471     471              
========================================
+ Hits         394     397       +3     
- Misses      3824    3828       +4     
  Partials      16      16              

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