Ensure all diagnostic services do not handle the same messages more than once

[DonJayamanne]

For #3502
Part 2

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• [no] Has a news entry file (remember to thank yourself!)
• [n/a] Has sufficient logging.
• [n/a] Has telemetry for enhancements.
• Unit tests & system/integration tests are added/updated
• [n/a] Test plan is updated as appropriate
• [n/a] package-lock.json has been regenerated by running npm install (if dependencies have changed)

[codecov]

Codecov Report

Merging #4038 into master will increase coverage by 14%.
The diff coverage is 67%.

@@           Coverage Diff            @@
##           master   #4038     +/-   ##
========================================
+ Coverage      66%     79%    +14%     
========================================
  Files         407     407             
  Lines       18583   18610     +27     
  Branches     2992    2996      +4     
========================================
+ Hits        12121   14581   +2460     
+ Misses       6461    4026   -2435     
- Partials        1       3      +2

Flag	Coverage Δ
#Linux	68% <37%> (+16%)	⬆️
#Windows	68% <37%> (+16%)	⬆️
#macOS	68% <37%> (?)