One shot CFB

[vcsjones]

This implements CFB one shots.

Some implementation notes:

1. As discovered in Persisted-key AesCng in CFB mode always uses CFB8 #55477, CFB128 and CFB64 do not work with persisted CNG keys, they always work in CFB8 mode today. Rather than replicating this wrong behavior, the AesCng and TripleDESCng one shots will throw if the key is persisted and the feedback size is other than 8. This limitation can be removed, if it is possible, when the linked issue is solved.
2. This does not change the behavior of the ICryptoTransform CFB implementation. The CNG CFB128 /CFB64 persisted-key remain as-is (using CFB8).
3. RC2 does not support CFB at all, so the implementation throws.

Closes#2406

[ghost]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, to please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[ghost]

Tagging subscribers to this area: @bartonjs, @vcsjones, @krwq, @GrabYourPitchforks
See info in area-owners.md if you want to be subscribed.

Issue Details

---

This implements CFB one shots.

Some implementation notes:

1. As discovered in Persisted-key AesCng in CFB mode always uses CFB8 #55477, CFB128 and CFB64 do not work with persisted CNG keys, they always work in CFB8 mode today. Rather than replicating this wrong behavior, AesCng and TripleDESCng will throw if the key is persisted and the feedback size is other than 8. This limitation can be removed, if it is possible, when the linked issue is solved.
2. RC2 does not support CFB at all, so the implementation throws.

Closes #2406

Author:	vcsjones
Assignees:	-
Labels:	area-System.Security, new-api-needs-documentation
Milestone:	-

[vcsjones]

Mono failures should be fixed by #55482.

[bartonjs]

Looks like all I had were a couple of nitpicky things. Nice work.

[bartonjs]

/azp run runtime-libraries-coreclr outerloop

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[vcsjones]

Seems like Pipeline's NuGet feed is cranky.

[bartonjs]

The outerloop failures aren't related, just waiting on the Linux-Debug leg to finish.