... Which will be needed for various reasons for Windows builds of certain
modularizations, which will otherwise complain that they can no longer
generate them as inlines.
In one case, deleted copies require explicitly defaulted moves, but they will
work as generated inline.
... Unnecessary because transitively included.
But each .cpp file still includes its own .h file near the top to ensure
that it compiles indenendently, even if it is reincluded transitively later.
