Better visibility to deprecations

Unfortunately, deprecation and removal is the main way I know to inform downstream consumers of breaking changes like these.

Yeah, it's a tough problem. But deprecated or not, I generally assume that core tools work. Version numbers in particular have been historically very lenient, so this is a really fundamental change that caught me off guard.

Build logs are noise, unless there's a problem. So while it's possible that I've seen the xxx is an invalid version and will not be supported in a future release warning flying by in the logs, to me, it isn't a call to action. It's just one line among hundreds.

Suffice to say, if something is going to break, I'd prefer a more detailed message, for example:

******************************************************************************** 
The version number <xxx> on package <yyy> package is no longer valid. 

By January 2023, you need to update version numbers to conform with PEP440 
or your builds may fail. You can retain the old behavior by passing 
the --allow-deprecated-version-numbers option to setup. 

See <some url> for details.
********************************************************************************

I'd also suggest putting the message at the end of the build log, not the beginning. Then it probably would be the first thing that I see after I run a build.

Originally posted by @sethrh in https://github.com/pypa/setuptools/issues/3772#issuecomment-1386427817

Start with the version-number warning described in the issue and review the linked discussion in issue #3772. Identify where that warning is emitted; done means the deprecation is presented as an actionable message with migration guidance, the opt-out option, and visibility at the end of the build log.