Refactor AnyConst{16,32} types

[Robbepop]

Pulled out from #1512.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.32%. Comparing base (b337e9b) to head (2a55fda).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1552      +/-   ##
==========================================
+ Coverage   72.29%   72.32%   +0.03%     
==========================================
  Files         179      179              
  Lines       16401    16318      -83     
==========================================
- Hits        11857    11802      -55     
+ Misses       4544     4516      -28     

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