* use the new http.Protocols to handle h1, h2 and h2c requests
* fix lint
* keep ConnCtxKey for now
* fix handling for h2c
* check http version while reading the connection
* check if connection implements connectionStater when it should
* add comments about either h1 or h2 must be used in the listener
* fix if check
* return a net.Conn that implements connectionStater if applicable
* remove http/1.1 from alpn if h1 is disabled
* fix matching if only h1 is enabled
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Co-authored-by: Matt Holt <mholt@users.noreply.github.com>