Implement PublicKeyComponents::build_encrypting_key

[Vadmeme]

Issues:

Resolves #581

Description of changes:

Adds a PublicKeyComponents::build_encrypting_key.

Call-outs:

N/A

Testing:

Im not sure how to implement unit tests for this change would need a reviewer to assist with this. I tested them in my personal application and they functioned as expected.

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 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 92.68%. Comparing base (c358484) to head (f407c0b).
Report is 116 commits behind head on main.

Files with missing lines	Patch %	Lines
aws-lc-rs/src/rsa/key.rs	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #582      +/-   ##
==========================================
- Coverage   95.80%   92.68%   -3.12%     
==========================================
  Files          61       67       +6     
  Lines        8143     9776    +1633     
  Branches        0     9776    +9776     
==========================================
+ Hits         7801     9061    +1260     
- Misses        342      429      +87     
- Partials        0      286     +286     

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