client: Add DialEarlyContext and DialAddrEarlyContext API

[VinozzZ]

Fixes #2812.

[codecov]

Codecov Report

Merging #2814 into master will decrease coverage by 2.30%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master    #2814      +/-   ##
==========================================
- Coverage   86.02%   83.72%   -2.30%     
==========================================
  Files         133      275     +142     
  Lines       12063    22189   +10126     
==========================================
+ Hits        10376    18576    +8200     
- Misses       1355     2906    +1551     
- Partials      332      707     +375     

Impacted Files	Coverage Δ
client.go	78.51% <50.00%> (+2.29%)	⬆️
internal/protocol/key_phase.go	80.00% <0.00%> (-20.00%)	⬇️
internal/testdata/cert.go	57.89% <0.00%> (-10.11%)	⬇️
internal/protocol/encryption_level.go	90.00% <0.00%> (-10.00%)	⬇️
internal/handshake/header_protector.go	78.26% <0.00%> (-6.81%)	⬇️
internal/handshake/retry.go	68.42% <0.00%> (-5.49%)	⬇️
closed_session.go	79.41% <0.00%> (-3.92%)	⬇️
buffer_pool.go	90.48% <0.00%> (-3.46%)	⬇️
internal/utils/buffered_write_closer.go	66.67% <0.00%> (-3.33%)	⬇️
http3/frames.go	74.60% <0.00%> (-3.04%)	⬇️
... and 262 more

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[marten-seemann]

Thank you! This lgtm, just one suggestion:

Can you use DialAddrEarlyContext in DialAddrEarly, in order to avoid code duplication?

func DialAddrEarly(...) {
     return DialAddrEarlyContext(context.Background(), ....)
}

[marten-seemann]

Thank you!