Use NuGet version of DocFX

[bkoelman]

Replace private binaries with the DocFX version on NuGet.

• Fixes namespace breadcrumb to omit links to non-existent pages
• Re-adds "Edit this page" links for source files that use source generators (partial auto-generated classes)
• Minor vertical whitespace fixes

Closes #2096.

QUALITY CHECKLIST

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.14%. Comparing base (4f787d3) to head (412b410).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2099   +/-   ##
=======================================
  Coverage   92.14%   92.14%           
=======================================
  Files         366      366           
  Lines       12124    12124           
  Branches     2038     2038           
=======================================
  Hits        11172    11172           
  Misses        584      584           
  Partials      368      368           

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