Use a Dynarray instead of a hashtable for the preprocessor locations

[WardBrian]

This hashtable only ever had keys that were numeric and growing, which means it was essentially just a growable array in a language without good support for those. Now that the standard library has a Dynarray module, we can use that and save on some storage

Submission Checklist

• Run unit tests
• Documentation
  • If a user-facing facing change was made, the documentation PR is here:
  • OR, no user-facing changes were made

Release notes

Copyright and Licensing

By submitting this pull request, the copyright holder is agreeing to
license the submitted work under the BSD 3-clause license (https://opensource.org/licenses/BSD-3-Clause)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.52%. Comparing base (39b9a75) to head (504585d).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1650   +/-   ##
=======================================
  Coverage   91.51%   91.52%           
=======================================
  Files          67       67           
  Lines        9975     9981    +6     
=======================================
+ Hits         9129     9135    +6     
  Misses        846      846           

Files with missing lines	Coverage Δ
src/core/Core.ml	100.00% <ø> (ø)
src/frontend/Preprocessor.ml	98.75% <100.00%> (+0.10%)	⬆️

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