feat: expose describeFieldTestCase for use in other packages

[wschurman]

Why

Separating this out from #138 so that the changelog can be updated and the new version can be released independently of the new IP field package.

How

Move function into its own file, add to index export.

Test Plan

yarn tsc

[codecov]

Codecov Report

Merging #139 (5ef7114) into master (5c7efe1) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #139      +/-   ##
==========================================
+ Coverage   95.80%   95.82%   +0.02%     
==========================================
  Files          70       72       +2     
  Lines        1810     1820      +10     
  Branches      223      225       +2     
==========================================
+ Hits         1734     1744      +10     
  Misses         75       75              
  Partials        1        1              

Flag	Coverage Δ
integration	95.82% <100.00%> (+0.02%)	⬆️
unittest	95.82% <100.00%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
packages/entity/src/EntityConfiguration.ts	100.00% <ø> (ø)
packages/entity/src/EntityFieldDefinition.ts	100.00% <100.00%> (ø)
packages/entity/src/EntityFields.ts	100.00% <100.00%> (ø)
packages/entity/src/EntityMutator.ts	98.20% <100.00%> (ø)
.../entity/src/utils/testing/describeFieldTestCase.ts	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5c7efe1...5ef7114. Read the comment docs.

[kgc00]