quic: http/3 headers behave differently than http/2

[martenrichter]

May be something not so important, but I stumpled upon it, when I tried to convert some http/2 code to http/3 code.

For http/2 headers[':status'] is numeric, while it is for http/3 a string.
You can also see it, if you compare the tests for the header fields.
I am not sure, if it is intentional, but I always thought the coding of http/3 headers is just the http/2 way.
This may be inconvenient for developers, so I do not have a strong opinion.
@jasnell
What do you think?
(And should I always mention you in the quic issues, or does it annoy more than help?).

[jasnell]

Always helps. I appreciate it. Honestly it's bugged me the way http2 handles it but I think I'm to blame for it lol. Would be a fairly simple fix at the c++ level, I think.

[martenrichter]

The question is, if one wants to fix it, though.
Changing http/2 is something one can no longer do today.
For http/3, one can have a different behavior. But there might be many who are used to http/2 behavior and then write issues....
(For me, it does not matter....)