The whole ownership model was getting a bit of a mess, with a some
of special cases to deal with. And I'm planning to make it even more
complex in the future.
So here is some upfront work to convert it over to reference counted
pointers.

This will be used for later refactoring for increased accuracy.

SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.

These aren't intended to be further specialized, so we can make this
obvious with final.

Removes constructors and destructors that don't actually provide any
behavior (i.e. doesn't constain generated code related to non-trivial
members in a cpp file, etc).

Lessens the amount of code present.