quic: expose QUIC certificates as JS X509Certificate, not raw handles

[pimterry]

Starting to work through the TLS implementation in QUIC, one nice small standalone fix here.

[nodejs-github-bot]

Review requested:

• @nodejs/quic

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.04%. Comparing base (b5da751) to head (4478d4b).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main   #63191    +/-   ##
========================================
  Coverage   90.03%   90.04%            
========================================
  Files         713      713            
  Lines      224510   224943   +433     
  Branches    42438    42528    +90     
========================================
+ Hits       202148   202542   +394     
- Misses      14163    14179    +16     
- Partials     8199     8222    +23     

Files with missing lines	Coverage Δ
lib/internal/quic/quic.js	100.00% <100.00%> (ø)

... and 45 files with indirect coverage changes

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