feat: add option to ignore enum values

[latonz]

Adds option to ignore enum values

Adds new attributes MapperIgnoreSourceValue and MapperIgnoreTargetValue to ignore source/target enum values. This is especially useful for strict enum mappings (to ignore single values not present in the source and/or target without emitting a diagnostic).

Fixes #337

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 #536 (3a2a29d) into main (85347e4) will decrease coverage by 0.98%.
The diff coverage is 89.07%.

@@            Coverage Diff             @@
##             main     #536      +/-   ##
==========================================
- Coverage   91.96%   90.99%   -0.98%     
==========================================
  Files         147      166      +19     
  Lines        4656     5606     +950     
  Branches      588      710     +122     
==========================================
+ Hits         4282     5101     +819     
- Misses        254      354     +100     
- Partials      120      151      +31     

Impacted Files	Coverage Δ
...y.Abstractions/MapperIgnoreSourceValueAttribute.cs	0.00% <0.00%> (ø)
...y.Abstractions/MapperIgnoreTargetValueAttribute.cs	0.00% <0.00%> (ø)
src/Riok.Mapperly/Helpers/HashHelper.cs	0.00% <0.00%> (ø)
...numerables/EnsureCapacity/EnsureCapacityBuilder.cs	45.94% <42.10%> (-32.32%)	⬇️
src/Riok.Mapperly/MapperResults.cs	50.00% <50.00%> (ø)
src/Riok.Mapperly/ImmutableEquatableArray.cs	54.54% <54.54%> (ø)
...ok.Mapperly/Configuration/AttributeDataAccessor.cs	68.88% <64.58%> (-7.93%)	⬇️
.../Descriptors/MappingBuilders/SpanMappingBuilder.cs	80.00% <80.00%> (ø)
.../Descriptors/MappingBuilders/EnumMappingBuilder.cs	84.75% <81.13%> (-7.01%)	⬇️
...lders/NewInstanceObjectMemberMappingBodyBuilder.cs	80.00% <83.33%> (+1.21%)	⬆️
... and 63 more

... and 2 files with indirect coverage changes

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[github-actions]

🎉 This PR is included in version 2.9.0-next.3 🎉

The release is available on:

• GitHub release
• v2.9.0-next.3

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 📦🚀