Investigate, Support and Build Tests for Fast Pimpl Use-case

[Twon]

Some references on fast pimpl: http://www.gotw.ca/gotw/028.htm https://www.bfilipek.com/2018/01/pimpl.html https://github.com/oliora/samples/blob/master/spimpl.h

In a post-C++ 11 world, this will need to handle meeting the alignment requirements of over-aligned type when alignment information is not available at the point of definition.