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 20.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 92.58%. Comparing base (c358484) to head (d0a9354).
Report is 105 commits behind head on main.

Files with missing lines	Patch %	Lines
aws-lc-rs/src/rsa/key.rs	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #582      +/-   ##
==========================================
- Coverage   95.80%   92.58%   -3.22%     
==========================================
  Files          61       67       +6     
  Lines        8143     9370    +1227     
  Branches        0     9370    +9370     
==========================================
+ Hits         7801     8675     +874     
- Misses        342      424      +82     
- Partials        0      271     +271     

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