sort type errors by comparing to input type

[nhuurre]

When typecheck fails for an overloaded Stan Math function, the five signatures listed aren't always the most relevant ones. This PR changes the error sorting heuristic to prefer the types that have a similar shape to the one supplied by the user. See bernoulli_logit in the tests for an example of how it looks.

Submission Checklist

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

Release notes

Copyright and Licensing

Copyright holder: Niko Huurre 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[bot]]

Codecov Report

Merging #1307 (08baffa) into master (c435684) will increase coverage by 0.01%. The diff coverage is 84.61%.

@@            Coverage Diff             @@
##           master    #1307      +/-   ##
==========================================
+ Coverage   89.00%   89.01%   +0.01%     
==========================================
  Files          64       64              
  Lines        9773     9777       +4     
==========================================
+ Hits         8698     8703       +5     
+ Misses       1075     1074       -1     

Impacted Files	Coverage Δ
src/middle/UnsizedType.ml	76.22% <66.66%> (+1.63%)	:arrow_up:
src/frontend/SignatureMismatch.ml	82.22% <90.00%> (-0.14%)	:arrow_down: