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.