Remove C++17 compatibility in version header file

[m-fila]

BEGINRELEASENOTES

• Removed C++17 compatibility in version header file

ENDRELEASENOTES

Since #343 we removed compatibility with older versions of C++, this can also go as now we have the spaceship operator

[jmcarcell]

While we are at this file I think https://github.com/key4hep/EDM4hep/blob/main/EDM4hepVersion.h.in#L78 can be consteval.

[tmadlener]

I am not sure if it makes sense to make the decode_version consteval. That would render it unusable in runtime contexts. But I am also not sure if we have actual use cases for that.

[tmadlener]

Nice. Thanks :)

[jmcarcell]

I am not sure if it makes sense to make the decode_version consteval. That would render it unusable in runtime contexts. But I am also not sure if we have actual use cases for that.

Yeah I'm not sure if there would be a case when the version would not be known at compile time, like reading it from a file...

[tmadlener]

I think if they are read from file, they will be split into major, minor, patch instead of being encoded into the 64 bit pre processor constant. I would leave it at constexpr for now (as we did with this PR).