Fix Storage Conversion generation bug

[matthchr]

If a map type is a TypeName that is not pointing to a local package, just use the type as is rather than trying to look it up (which will fail).

[codecov-commenter]

Codecov Report

Merging #1595 (1f1ae37) into master (d420499) will increase coverage by 0.02%.
The diff coverage is 88.88%.

@@            Coverage Diff             @@
##           master    #1595      +/-   ##
==========================================
+ Coverage   63.22%   63.25%   +0.02%     
==========================================
  Files         183      183              
  Lines       11903    11918      +15     
==========================================
+ Hits         7526     7539      +13     
- Misses       3704     3706       +2     
  Partials      673      673              

Impacted Files	Coverage Δ
...enerator/pkg/codegen/storage/property_converter.go	0.00% <0.00%> (ø)
hack/generator/pkg/astbuilder/builder.go	85.09% <100.00%> (+0.37%)	⬆️
hack/generator/pkg/astmodel/type_name.go	63.49% <100.00%> (+3.14%)	⬆️
.../generator/pkg/conversions/property_conversions.go	78.68% <100.00%> (+0.21%)	⬆️

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[matthchr]

Thanks @theunrepentantgeek for the push to the branch with additional tests and some extra fixes