Add as_str to Version type

[itsibitzi]

Stringifications of the variants of the Version are known at compile time so requiring a Debug format is not necessary.

This is nice for me specifically because I want to record the HTTP version of queries using metrics crate. This crate allows users to record labels as either a String or &'static str, and given I didn't want to allocate a String with the Debug format I had to copy-paste the lookup.

[seanmonstar]

Thanks for the PR!

My feeling is that an as_str() doesn't fit semantically. Is there some sort of true string representation of a Version? I don't think there is.

The way I would solve this myself in another crate is to just match and return some static strings that make sense for my metrics.

[itsibitzi]

Yep, I'm doing the match statement right now. :)

I thought it might be useful for others to have access to the mapping currently within debug, but statically. The RFCs standardizing HTTP seem to use the HTTP/xyz format so I felt that was a canonical-enough form and would save some folks writing (admittedly a small amount of) boiler plate. Though I do note that the previous Debug implementation referred to HTTP/2 as HTTP/2.0, and similar for HTTP/3, which is not what the RFC used. This could be corrected either in both or just in an as_str version.

The function doesn't need to be called as_str, I suppose, but I'm not sure what would be a better name that would be easy for people to find. as_rfc_name? as_name?