net/http: move HTTP/2 into std

[neild]

The net/http package includes transparent support for HTTP/2. The source of truth for this implementation is the golang.org/x/net/http2 package, which is vendored into std (using a rather complicated process to avoid import cycles). The http2 package also exposes a number of configuration settings and features which are not directly accessible from net/http.

There were good reasons for starting development of the HTTP/2 implementation outside of std, but the current state of affairs is confusing and inconvenient. Backporting HTTP/2 fixes into minor releases is difficult. New versions of net/http need to support old versions of x/net. We can't make changes to the HTTP/1 and HTTP/2 implementations atomically. Users need to import an x/ package to configure HTTP/2 settings.

This issue is a tracking issue for moving HTTP/2 into std.

The desired end state is that the canonical HTTP/2 implementation used by net/http is located in the main Go repository and golang.org/x/net/http2 is deprecated.

The golang.org/x/net/http2 package has a substantial API surface. Some of that functionality (such as server and client configuration settings) will be made available via net/http, some will move into new packages, and some will be deprecated. The first stage of this project is to make every non-deprecated feature of golang.org/x/net/http2 available elsewhere.

(Original discussion: #60746)

• x/net/http2: add per-write timeouts (WriteByteTimeout) #61777
• x/net/http2: configurable server pings #67812
• net/http: HTTP/2 configuration API #67813
• net/http: HTTP version selection API #67814
• net/http: new protocol registration mechanism #69649
• net/http: support unencrypted HTTP/2 (h2c) #67816
• proposal: x/net/http2: deprecate WriteScheduler #67817
• x/net/http2: move frame operations to x/net/http2/http2frame #67819