Refactor JWX logic to reduce dep on JWX lib

[decentralgabe]

Fixes #365

[codecov-commenter]

Codecov Report

Merging #368 (208d36b) into main (da47a51) will increase coverage by 0.14%.
The diff coverage is 60.30%.

@@            Coverage Diff             @@
##             main     #368      +/-   ##
==========================================
+ Coverage   59.14%   59.28%   +0.14%     
==========================================
  Files          56       56              
  Lines        6890     6847      -43     
==========================================
- Hits         4075     4059      -16     
+ Misses       2094     2076      -18     
+ Partials      721      712       -9     

Impacted Files	Coverage Δ
crypto/jwx/jws.go	26.83% <0.00%> (ø)
crypto/keys.go	85.84% <ø> (ø)
credential/jws.go	48.78% <25.00%> (-3.85%)	⬇️
crypto/jwx/jwt.go	52.31% <56.92%> (+4.53%)	⬆️
credential/jwt.go	40.43% <59.09%> (+1.86%)	⬆️
credential/exchange/request.go	40.70% <61.54%> (+0.45%)	⬆️
cryptosuite/jsonwebkey2020.go	46.10% <61.54%> (-1.38%)	⬇️
crypto/jwx/jwk.go	55.94% <62.41%> (-0.14%)	⬇️
credential/exchange/submission.go	72.87% <100.00%> (ø)
credential/signature.go	80.00% <100.00%> (ø)
... and 4 more