Improve build hygiene and filename utility coverage

[fred-vu]

Improve build hygiene and filename utility coverage

[peazip]

Thank you very much for the commit, it contains various good suggestions.
However, as it covers various distinct topics, I would prefer to test each logical portion separately instead of merging all changes at once - especially as the PeaZip.ShellEx part was originally user contributed (so it is quite outside my usual coding style comfort zone), and the file name routines being security-sensitive and needing extensive testing for smallest changes.
I'll look deeper at the changes to organize the testing and deployment of the various contributions in the code base.