wireprotov2: send content encoded frames from server Now that we have support for negotiating encodings and configuring an encoder, we can start sending content encoded frames from the server. This commit teaches the wireprotov2 server code to send content encoded frames. On the mozilla-unified repository with zstd enabled peers, this change reduces the total amount of data transferred from server to client drastically: befor: 7,190,995,812 bytes after: 1,605,508,691 bytes Differential Revision: https://phab.mercurial-scm.org/D4927