net/http: use consistent IDNA processing for dial target and Host header

[kingljl]

Changes:

• src/net/http/request.go: add idnaASCIIHostPort and use it for the HTTP/1
  Host header instead of httpguts.PunycodeHostPort.
• src/net/http/internal/httpcommon/httpcommon.go: use idnaASCIIHostPort
  for the HTTP/2 :authority in EncodeHeaders (bundled copy).
• src/vendor/golang.org/x/net/internal/httpcommon/request.go: same change
  in the vendored source of the bundle (see net/http: use consistent IDNA processing for dial target and Host header net#253).
• src/net/http/internal/http2/transport.go: map authorityAddr with
  idna.Lookup.ToASCII so the h2 connection-pool key matches the dial and
  header.
• src/net/http/transport_test.go: add TestTransportIDNAMapping covering
  HTTP/1 and HTTP/2.

For golang/net#253
Fixes #80417

[gopherbot]

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