Remove napi functions from NexusClasses

[rboston628]

Description of work

Summary of work

This finishes un-reverting work in PR #38791 .

This will remove all instances of napi functions from NexusClasses, which also finishes the process of consolidating access of NeXus through NeXus::File.

The NXDataSetTyped::load method was gently refactored to remove the k,l parameters, which are never used, as well as the branching logic for those being non-negative, which never happened.

Changes to NeXus::File are minimal, including adding additional constructors, and an assignment operator.

Related to #38332

Further detail of work

To test:

Windows build from commit bfd6f25 (NOT tip of branch)

Windows build NOT re-run on commit de12700, but this should not impact any behavior.

---

Reviewer

Please comment on the points listed below (full description).
Your comments will be used as part of the gatekeeper process, so please comment clearly on what you have checked during your review. If changes are made to the PR during the review process then your final comment will be the most important for gatekeepers. In this comment you should make it clear why any earlier review is still valid, or confirm that all requested changes have been addressed.

Code Review

• Is the code of an acceptable quality?
• Does the code conform to the coding standards?
• Are the unit tests small and test the class in isolation?
• If there is GUI work does it follow the GUI standards?
• If there are changes in the release notes then do they describe the changes appropriately?
• Do the release notes conform to the release notes guide?

Functional Tests

• Do changes function as described? Add comments below that describe the tests performed?
• Do the changes handle unexpected situations, e.g. bad input?
• Has the relevant (user and developer) documentation been added/updated?

Does everything look good? Mark the review as Approve. A member of @mantidproject/gatekeepers will take care of it.

Gatekeeper

If you need to request changes to a PR then please add a comment and set the review status to "Request changes". This will stop the PR from showing up in the list for other gatekeepers.

[peterfpeterson]

I knew this day would come eventually

[peterfpeterson]

Changing the NXhandle to shared_ptr<::NeXus::File> is a great way to make sure things get cleaned up with less effort. I also like that you removed some (not used by the outside) variables from load() and cleaned up the method. I didn't realize how many different copy constructors would be needed for shared_ptr.