use the new qtls interface for (re)storing app data with a session state

[marten-seemann]

Depends on #2628. Fixes #2491.

Application data is now retrieved and restored via two callbacks on the qtls.Config. This allows us the get rid of the rather complex wrapping of the qtls.ClientSessionCache. Furthermore, it makes sure that we only restore the application data when qtls decides to actually use the ticket.

[codecov]

Codecov Report

Merging #2631 into master will increase coverage by 0.06%.
The diff coverage is 84.44%.

@@            Coverage Diff             @@
##           master    #2631      +/-   ##
==========================================
+ Coverage   86.29%   86.35%   +0.06%     
==========================================
  Files         121      120       -1     
  Lines        9775     9744      -31     
==========================================
- Hits         8435     8414      -21     
+ Misses        998      993       -5     
+ Partials      342      337       -5     

Impacted Files	Coverage Δ
internal/handshake/unsafe.go	66.67% <ø> (+6.67%)	⬆️
internal/handshake/crypto_setup.go	66.95% <66.67%> (+0.42%)	⬆️
internal/handshake/qtls.go	90.76% <100.00%> (+1.04%)	⬆️
internal/handshake/session_ticket.go	100.00% <100.00%> (ø)
internal/wire/transport_parameters.go	89.72% <100.00%> (-0.08%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f926945...07d4fd0. Read the comment docs.