fix: generate correct nullability for external array elements

[TimothyMakkison]

Generate correct nullability for external array elements

Description

Using ImplementsGeneric on external types will erase the nullable annotation of an array element type. This is used in CollectionInfosBuilder.GetEnumeratedType where the resulting enumerated type is used by EnumerableMappingBuilder to map the element types of two collections.

This caused a rare issue where an array collection would be treated as if it had a nullable element type.

Fixes #690

Checklist

• The existing code style is followed
• The commit message follows our guidelines
• Performed a self-review of my code
• Hard-to-understand areas of my code are commented

[codecov]

Codecov Report

Merging #715 (3b461a5) into main (44b5df9) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #715   +/-   ##
=======================================
  Coverage   91.15%   91.15%           
=======================================
  Files         198      198           
  Lines        6555     6557    +2     
  Branches      815      816    +1     
=======================================
+ Hits         5975     5977    +2     
  Misses        389      389           
  Partials      191      191           

Files Changed	Coverage Δ
...y/Descriptors/Enumerables/CollectionInfoBuilder.cs	96.64% <100.00%> (+0.02%)	⬆️

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[github-actions]

🎉 This PR is included in version 3.2.0-next.2 🎉

The release is available on:

• GitHub release
• v3.2.0-next.2

Your semantic-release bot 📦🚀

[github-actions]

🎉 This PR is included in version 3.2.0 🎉

The release is available on:

• GitHub release
• v3.2.0

Your semantic-release bot 📦🚀