Expose builtin constraints

[WardBrian]

Closes #1436

This needs some math work before merging, at the very least stan-dev/math#3151

Submission Checklist

• Run unit tests
• Documentation
  • If a user-facing facing change was made, the documentation PR is here: Forthcoming

Release notes

All the built-in constraint types now have corresponding _jacobian, _constrain, and _unconstrain functions. The first two functions are identical except for the _jacobian version will increment the target with the necessary change of variables adjustment.

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 90.56%. Comparing base (c397822) to head (e68e038).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1494      +/-   ##
==========================================
+ Coverage   90.46%   90.56%   +0.09%     
==========================================
  Files          66       66              
  Lines       10712    10809      +97     
==========================================
+ Hits         9691     9789      +98     
+ Misses       1021     1020       -1     

Files with missing lines	Coverage Δ
src/frontend/Typechecker.ml	93.10% <100.00%> (+0.03%)	⬆️
src/middle/Stan_math_signatures.ml	98.24% <100.00%> (+0.13%)	⬆️
src/stan_math_backend/Lower_expr.ml	93.65% <100.00%> (+0.08%)	⬆️

... and 1 file with indirect coverage changes

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[WardBrian]

The expression test failures are kind of weird but they seem to be fixed by stan-dev/math#3147 so there might just be some known bug in offset_multipliers code (cc @SteveBronder)