Backport various fixes and enhancements from other work in progress

[bkoelman]

See the individual commits for details.

QUALITY CHECKLIST

• Changes implemented in code
• Complies with our contributing guidelines
• Adapted tests
• N/A: Documentation updated

[codecov]

Codecov Report

Attention: Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 90.39%. Comparing base (e8e3093) to head (b67dd43).
Report is 1 commits behind head on openapi.

Files with missing lines	Patch %	Lines
...e.OpenApi.Swashbuckle/OpenApiEndpointConvention.cs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           openapi    #1685      +/-   ##
===========================================
- Coverage    90.40%   90.39%   -0.01%     
===========================================
  Files          461      461              
  Lines        14043    14046       +3     
  Branches      2190     2190              
===========================================
+ Hits         12695    12697       +2     
- Misses         913      914       +1     
  Partials       435      435              

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