Broader Ed25519 Key Format Support

[skmcgrail]

Description of changes:

• Similar goal to Support for compressed and X.509 public key format #498
• Support parsing of raw ED25519 public keys or X.509 SubjectPublicInfo when performing signature validation
• Support for X.509 SubjectPublicInfo serialization for ED25519 PublicKey using AsDer trait.
• Add support for the AsDer for PKCS#8 v1 and v2 for Ed25519KeyPair for consistency with our serialization trait design.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 89.88764% with 18 lines in your changes missing coverage. Please review.

Project coverage is 92.48%. Comparing base (c358484) to head (c3f2c45).
Report is 78 commits behind head on main.

Files with missing lines	Patch %	Lines
aws-lc-rs/src/ed25519.rs	90.22%	6 Missing and 11 partials ⚠️
aws-lc-rs/src/ec/key_pair.rs	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #506      +/-   ##
==========================================
- Coverage   95.80%   92.48%   -3.32%     
==========================================
  Files          61       67       +6     
  Lines        8143     9235    +1092     
  Branches        0     9235    +9235     
==========================================
+ Hits         7801     8541     +740     
- Misses        342      422      +80     
- Partials        0      272     +272     

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