Pretty/Flatten Events by Type when Stringified

[alexanderbez]

When events are stringified, they'll be easier to read if they're grouped by unique type.

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• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.

• Wrote tests

• Updated relevant documentation (docs/)

• Added a relevant changelog entry: clog add [section] [stanza] [message]

• rereviewed Files changed in the github PR explorer

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For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
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[fedekunze]

LGTM

[codecov]

Codecov Report

Merging #4648 into master will increase coverage by 0.14%.
The diff coverage is 90.9%.

@@            Coverage Diff             @@
##           master    #4648      +/-   ##
==========================================
+ Coverage   54.83%   54.97%   +0.14%     
==========================================
  Files         272      272              
  Lines       17020    17027       +7     
==========================================
+ Hits         9333     9361      +28     
+ Misses       7001     6980      -21     
  Partials      686      686