http3: add compatibility with net/http.ResponseController

[dunglas]

Go 1.20 added a new "net/http".ResponseController type that allows, among other things, to set per-request timeouts.

This patch adds support for this new type. It is necessary for caddyserver/caddy#5509 and dunglas/mercure#764.

[codecov]

Codecov Report

Merging #3790 (e0f4cc7) into master (4a2a574) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3790      +/-   ##
==========================================
+ Coverage   84.23%   84.26%   +0.03%     
==========================================
  Files         142      140       -2     
  Lines       14084    14046      -38     
==========================================
- Hits        11863    11835      -28     
+ Misses       1801     1793       -8     
+ Partials      420      418       -2     

Impacted Files	Coverage Δ
http3/response_writer.go	85.06% <100.00%> (+0.91%)	⬆️

... and 4 files with indirect coverage changes

[marten-seemann]

Is there a better way to test this? All you're currently testing is that the response writer exposes the deadline functions.

Should we have an integration test in integrationtests/self/http_test.go?

[dunglas]

@marten-seemann better integration tests added (I also tested manually that this patch works well with Mecure and Caddy).

[marten-seemann]

Thank you @dunglas!