implement QUIC v2

[marten-seemann]

Fixes #3412.

[codecov]

Codecov Report

Merging #3432 (c5ee496) into master (8185d1b) will decrease coverage by 0.02%.
The diff coverage is 89.69%.

@@            Coverage Diff             @@
##           master    #3432      +/-   ##
==========================================
- Coverage   85.44%   85.42%   -0.02%     
==========================================
  Files         136      136              
  Lines        9946     9989      +43     
==========================================
+ Hits         8498     8533      +35     
- Misses       1066     1074       +8     
  Partials      382      382              

Impacted Files	Coverage Δ
internal/wire/header.go	86.96% <76.00%> (-3.37%)	⬇️
internal/wire/extended_header.go	87.14% <80.00%> (-0.45%)	⬇️
http3/server.go	72.61% <100.00%> (-0.09%)	⬇️
internal/handshake/aead.go	98.11% <100.00%> (+0.20%)	⬆️
internal/handshake/crypto_setup.go	66.82% <100.00%> (ø)
internal/handshake/header_protector.go	80.00% <100.00%> (+1.74%)	⬆️
internal/handshake/initial_aead.go	100.00% <100.00%> (ø)
internal/handshake/updatable_aead.go	96.45% <100.00%> (+0.03%)	⬆️
internal/protocol/version.go	94.59% <100.00%> (+0.31%)	⬆️

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[mattrobenolt]

I'm guessing this is minor, but after this change, we get duplicate values in the Alt-Svc header due to generateAltSvcHeader() spitting back duplicate h3 values because of Version1 and Version2 both being coalesced to h3.

As a concrete example:

alt-svc: h3=":8080"; ma=2592000,h3=":8080"; ma=2592000,h3-29=":8080"; ma=2592000

is what I'm getting now, notice how there are two identical h3 values.

I'm happy to submit a PR for this.