fix: restore Slice Zone Slices union in `Content`

[angeloashmore]

Types of changes

• [ ] Chore (a non-breaking change which is related to package maintenance)
• [x] Bug fix (a non-breaking change which fixes an issue)
• [ ] New feature (a non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Description

This PR restores a type export in the Content namespace representing Slice Zone choices. The type was inadvertantly removed in v0.1.12.

Checklist:

• [ ] My change requires an update to the official documentation.
• [x] All TSDoc comments are up-to-date and new ones have been added where necessary.
• [x] All new and existing tests are passing.

[codecov-commenter]

Codecov Report

Merging #57 (d4806c2) into main (3793c9f) will increase coverage by 0.04%. Report is 1 commits behind head on main. The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main      #57      +/-   ##
==========================================
+ Coverage   97.06%   97.10%   +0.04%     
==========================================
  Files          20       20              
  Lines        1464     1486      +22     
  Branches      161      161              
==========================================
+ Hits         1421     1443      +22     
  Misses         42       42              
  Partials        1        1              

Files Changed	Coverage Δ
src/generateTypes.ts	100.00% <100.00%> (ø)
src/lib/buildCustomTypeDataType.ts	100.00% <100.00%> (ø)
src/lib/buildCustomTypeType.ts	100.00% <100.00%> (ø)
src/lib/buildFieldProperties.ts	97.09% <100.00%> (+0.04%)	:arrow_up:
src/lib/buildSharedSliceType.ts	93.66% <100.00%> (+0.23%)	:arrow_up: