Laplace sampling: change output columns for consistency

[WardBrian]

Submission Checklist

• Run unit tests: ./runTests.py src/test/unit
• Run cpplint: make cpplint
• Declare copyright holder and open-source license: see below

Summary

Closes #3183. This changes the names of the log_p and log_q output columns to log_p__ and log_q__, and moves them to the start to match up with other algorithms.

Unfortunately this was not caught before release, but because cmdstanpy and cmdstanr don't have support for this built-out yet I think we can say that it is a bug fix rather than a breaking change, and release it in 2.32.1 next week (see stan-dev/cmdstan#1154)

I believe the CmdStan implementation also assumes this ordering in its tests, so those may briefly break if we merge this.

Documentation

The docs page (https://mc-stan.org/docs/cmdstan-guide/laplace-sampling.html) will need to be updated

Copyright and Licensing

Please list the copyright holder for the work you are submitting (this will be you or your assignee, such as a university or company):

Simons Foundation

By submitting this pull request, the copyright holder is agreeing to 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/)

[mitzimorris]

LGTM!