Implement PKCS7_verify, update PKCS7_sign

[WillChilds-Klein]

Notes

This PR implements PKCS7_verify for verifying signedData-type PKCS7 messages. It also adds another mode of operation to PKCS7_sign for compatibility with Ruby. Flags for these functions are documented in header comments.

We also remove most support for signedAndEnveloped-type PKCS7 messges, as they're not required by Ruby's tests beyond a few getters/setters. OpenSSL supports this type in PKCS7_decrypt but not PKCS7_verify, PKCS7_sign, nor PKCS7_encrypt, so it's unclear what (if any) role signedAndEnveloped types have with respect to these functions. If we wish to revisit support for this type in the future, I have a branch here implementing encrypt/decrypt/sign/verify support and a test.

Lastly, we externalize some of the previously internal PKCS7 ASN.1/struct definitions as ruby's source accesses some of their members directly.

Testing

• unit tests
• with ruby source patch and integration test from this branch, ran ruby's PKCS7 test suite against this PR's contents

$ time ./tests/ci/integration/run_ruby_integration.sh ruby_3_1
...
# Running tests:

Finished tests in 0.160404s, 81.0451 tests/s, 579.7843 assertions/s.
13 tests, 93 assertions, 0 failures, 0 errors, 1 skips

ruby -v: ruby 3.1.6p260 (2024-12-03 revision 326a6cbf9b) [x86_64-linux]
+ popd
~/aws-lc/RUBY_BUILD_ROOT/ruby-src ~/aws-lc/RUBY_BUILD_ROOT
+ popd
~/aws-lc/RUBY_BUILD_ROOT

real    4m13.491s
user    6m35.828s
sys     1m3.948s

---

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 79.74277% with 63 lines in your changes missing coverage. Please review.

Project coverage is 78.76%. Comparing base (2a72226) to head (f66e6ef).
Report is 16 commits behind head on main.

Files with missing lines	Patch %	Lines
crypto/pkcs7/pkcs7.c	75.15%	39 Missing ⚠️
crypto/pkcs7/pkcs7_x509.c	72.13%	17 Missing ⚠️
crypto/test/test_util.cc	66.66%	4 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1993      +/-   ##
==========================================
+ Coverage   78.68%   78.76%   +0.07%     
==========================================
  Files         598      598              
  Lines      103323   103620     +297     
  Branches    14686    14738      +52     
==========================================
+ Hits        81301    81617     +316     
+ Misses      21372    21351      -21     
- Partials      650      652       +2     

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