Add end-to-end testing to the definition of done for .NET Analyzers

[jeffhandley]

To help address issues like #5636, this adds end-to-end testing notes into the definition of done for .NET Analyzers. This captures how that specific issue was discovered, reproduced, and narrowed down.

[codecov]

Codecov Report

Merging #5640 (902fb40) into main (0a03ab2) will increase coverage by 0.00%.
The diff coverage is n/a.

❗ Current head 902fb40 differs from pull request most recent head f90e9d5. Consider uploading reports for the commit f90e9d5 to get more accurate results

@@           Coverage Diff           @@
##             main    #5640   +/-   ##
=======================================
  Coverage   95.54%   95.55%           
=======================================
  Files        1275     1275           
  Lines      292160   292160           
  Branches    17612    17612           
=======================================
+ Hits       279158   279163    +5     
+ Misses      10615    10605   -10     
- Partials     2387     2392    +5