Vectorize conj

[WardBrian]

Summary

This vectorizes the conj function.

Tests

This did a minor re-write of the vectorization test framework to add the option for functions which only support complex inputs.
This changed the enum we use for settings accordingly:

-enum class PromoteToComplex { No, Yes };
+enum class ScalarSupport { Real, RealAndComplex, ComplexOnly };

Side Effects

Many test files changed as part of that renaming, but none of them changed in meaning.

Release notes

The conj function is vectorized for Eigen and std::vector types.

Checklist

• Math issue: Closes Vectorize complex conjugate operation #2815

• Copyright holder: Simons Foundation

  The copyright holder is typically you or your assignee, such as a university or company. By submitting this pull request, the copyright holder is agreeing to the license the submitted work under the following licenses:
  - Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
  - Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

• the basic tests are passing

  • unit tests pass (to run, use: ./runTests.py test/unit)
  • header checks pass, (make test-headers)
  • dependencies checks pass, (make test-math-dependencies)
  • docs build, (make doxygen)
  • code passes the built in C++ standards checks (make cpplint)

• the code is written in idiomatic C++ and changes are documented in the doxygen

• the new changes are tested

[WardBrian]

After a bunch of CI issues this is finally passing and ready for review

[SteveBronder]

Looks good!