Add intermediate data structure for attested credential data

[Firehed]

Rather than having the AuthenticatorData build the Credential during registration, it's now being adjusted to instead return the underlying components that it will need.

While this is a minor structural formality right now, it will ease the adoption of the updated credential storage recommendations described in the Level 3 version of the spec that are not captured in the current L2-based implementation.

[codecov]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (a0562be) 81.27% compared to head (f76b47f) 81.03%.

Files	Patch %	Lines
src/Attestations/FidoU2F.php	0.00%	3 Missing ⚠️
src/AttestedCredentialData.php	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main      #52      +/-   ##
============================================
- Coverage     81.27%   81.03%   -0.24%     
- Complexity      207      208       +1     
============================================
  Files            24       25       +1     
  Lines           614      617       +3     
============================================
+ Hits            499      500       +1     
- Misses          115      117       +2     

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