Libmoinfo rework, part 2

[TiborGY]

Description

This is the continuation of my previous MOInfo PR #3112, with the following general themes:

• Adding new docstrings and making existing ones machine readable for VS Code (and probably also Doxygen)
• Rebalancing the class hierarchy by sinking things that get reused to the base class, and hoisting things up in the inheritance chain that only get used in one derived class
• Reducing visible and mutable state, as well as the contact surface of the classes. This is achieved by making data and functions as private as possible, providing access to data through getters returning const& when necessary, and making a few data members const. Having const members in classes is sometimes considered to be bad form, but AFAIK all of the downsides are already incurred on account of MOInfoBase having reference members.

The git history on this branch is admittedly a bit messy, I changed my mind about a couple of things. LMK if that is a problem.
The next PR in this series will get to what I originally wanted to achieve and remove uses of the ugly "cast Dimension object to pointer" operators (see #2953) from libmoinfo.

User API & Changelog headlines

• No API changes

Dev notes & details

• Unused function MOInfoBase::correlate is removed
• The only thing the MOInfoBase dtor does is call MOInfoBase::cleanup(), an empty function. Removed both.
• Moved the contents of MOInfo::free_memory() into its only caller, the MOInfo dtor
• Added a lot of new machine-readable docstrings, moved some existing ones
• Some "obsolete code", commented out a long time ago is deleted from moinfo_mappings.cc
• Moved the double** scf MO array and the get_scf_mos() getter from MOInfoBase to MOInfo and made the array private
• Moved the contents of MOInfoBase::startup() into its only caller, the MOInfoBase ctor
• Moved MOInfoBase::nmo to MOInfo and made it private
• Made the molecular charge const and private in MOInfoBase
• Made MOInfoBase::sopi private, added a protected getter fn to give access in derived classes
• Made MOInfoBase::nso, MOInfoBase::nuclear_energy and MOInfoBase::irr_labs private
• All functions in MOInfoBase that have previously returned copies of std::vector members now return const& to the vector in the object, avoiding a potential copy.
• Since MOInfoBase::silent is only used in the ctor of MOInfo,, I removed it from MOInfoBase and MOInfoSCF
• Inlined MOInfo::get_actv(size_t i) and MOInfo::get_docc(size_t i) as both were only called once. Since these overloads are now gone from MOInfo, it can now just use get_docc() and get_actv() from MOInfoBase instead of having to reimplement or explicitly inherit them.

Checklist

• No new features
• Tests run by the CI are passing
• Errors in the full test suite appear to be unrelated to libmoinfo

Status

• Ready for review
• Ready for merge

[loriab]

Thanks, this lgtm! Needs a review by someone closer to libmoinfo and mcscf, probably FAE.

[JonathonMisiewicz]

LGTM! @loriab, Francesco is going to be out of commission until June 8th, so I suggest we merge without him. Your call.