feat: explicit enum mappings for byValue enum mappings

[latonz]

explicit enum mappings for byValue enum mappings

Fixes #482

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
• The documentation is updated (as applicable)
• Unit tests are added/updated
• Integration tests are added/updated (as applicable, especially if feature/bug depends on roslyn or framework version in use)

[codecov]

Codecov Report

Merging #489 (9e65cbc) into main (b17f666) will increase coverage by 0.36%.
The diff coverage is 94.65%.

@@            Coverage Diff             @@
##             main     #489      +/-   ##
==========================================
+ Coverage   92.08%   92.45%   +0.36%     
==========================================
  Files         135      141       +6     
  Lines        4282     4491     +209     
  Branches      591      573      -18     
==========================================
+ Hits         3943     4152     +209     
- Misses        225      226       +1     
+ Partials      114      113       -1     

Impacted Files	Coverage Δ
...iok.Mapperly.Abstractions/MapEnumValueAttribute.cs	0.00% <0.00%> (ø)
...scriptors/InlineExpressionMappingBuilderContext.cs	95.12% <ø> (ø)
...appingBodyBuilders/UserMethodMappingBodyBuilder.cs	90.47% <ø> (ø)
...Riok.Mapperly/Descriptors/MappingBuilderContext.cs	98.14% <ø> (ø)
...erly/Descriptors/MappingBuilders/MappingBuilder.cs	100.00% <ø> (ø)
src/Riok.Mapperly/Descriptors/MappingCollection.cs	100.00% <ø> (ø)
...iok.Mapperly/Descriptors/Mappings/MethodMapping.cs	95.00% <ø> (ø)
...Mappings/UserDefinedExistingTargetMethodMapping.cs	87.17% <ø> (ø)
...serMappings/UserDefinedNewInstanceMethodMapping.cs	100.00% <ø> (ø)
...pings/UserMappings/UserImplementedMethodMapping.cs	90.90% <ø> (ø)
... and 38 more

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[github-actions]

🎉 This PR is included in version 2.9.0-next.2 🎉

The release is available on:

• GitHub release
• v2.9.0-next.2

Your semantic-release bot 📦🚀

[github-actions]

🎉 This PR is included in version 3.0.0 🎉

The release is available on:

• GitHub release
• v3.0.0

Your semantic-release bot 📦🚀