enum is defined check and fallback values

[latonz]

enum is defined check and fallback values

Fixes #488

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 #491 (1dfc785) into main (b17f666) will decrease coverage by 0.14%.
The diff coverage is 91.93%.

@@            Coverage Diff             @@
##             main     #491      +/-   ##
==========================================
- Coverage   92.08%   91.95%   -0.14%     
==========================================
  Files         135      147      +12     
  Lines        4282     4647     +365     
  Branches      591      586       -5     
==========================================
+ Hits         3943     4273     +330     
- Misses        225      254      +29     
- Partials      114      120       +6     

Impacted Files	Coverage Δ
src/Riok.Mapperly.Abstractions/MapEnumAttribute.cs	0.00% <0.00%> (-100.00%)	⬇️
...iok.Mapperly.Abstractions/MapEnumValueAttribute.cs	0.00% <0.00%> (ø)
...scriptors/InlineExpressionMappingBuilderContext.cs	95.12% <ø> (ø)
...appingBodyBuilders/UserMethodMappingBodyBuilder.cs	90.47% <ø> (ø)
...tors/MappingBuilders/EnumToStringMappingBuilder.cs	100.00% <ø> (ø)
...erly/Descriptors/MappingBuilders/MappingBuilder.cs	100.00% <ø> (ø)
src/Riok.Mapperly/Descriptors/MappingCollection.cs	100.00% <ø> (ø)
...ptors/Mappings/Enums/EnumFromStringParseMapping.cs	65.21% <ø> (ø)
.../Descriptors/Mappings/Enums/EnumToStringMapping.cs	100.00% <ø> (ø)
...iok.Mapperly/Descriptors/Mappings/MethodMapping.cs	95.00% <ø> (ø)
... and 53 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 📦🚀