wireproto: extract HTTP version 2 code to own module wireprotoserver has generic and version 1 server code. The wireproto module also has both version 1 and version 2 command implementations. Upcoming work I want to do will make it difficult for this code to live in the current locations. Plus, it kind of makes sense for the version 2 code to live in an isolated module. This commit copies the HTTPv2 bits from wireprotoserver into a new module. We do it as a file copy to preserve history. A future commit will be copying wire protocol commands into this module as well. But there is little history of that code, so it makes sense to take history for wireprotoserver. Differential Revision: https://phab.mercurial-scm.org/D3230

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