Return DSA and ECDSA keys from certificate in SignedXml.

[vcsjones]

If the X.509 certificate has a DSA or ECDSA public key, return them if they are available.

Closes #55194

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I was able to add a test case for DSA, prior to the fix the test fails with:

 Error Message:
   System.ArgumentNullException : Value cannot be null. (Parameter 'key')
  Stack Trace:
     at System.Security.Cryptography.Xml.SignedXml.CheckSignedInfo(AsymmetricAlgorithm key) in /workspaces/runtime/src/libraries/System.Security.Cryptography.Xml/src/System/Security/Cryptography/Xml/SignedXml.cs:line 998
   at System.Security.Cryptography.Xml.SignedXml.CheckSignature(AsymmetricAlgorithm key) in /workspaces/runtime/src/libraries/System.Security.Cryptography.Xml/src/System/Security/Cryptography/Xml/SignedXml.cs:line 283

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Issue Details

---

If the X.509 certificate has a DSA or ECDSA public key, return them if they are available.

Closes #55194

---

I was able to add a test case for DSA, prior to the fix the test fails with:

 Error Message:
   System.ArgumentNullException : Value cannot be null. (Parameter 'key')
  Stack Trace:
     at System.Security.Cryptography.Xml.SignedXml.CheckSignedInfo(AsymmetricAlgorithm key) in /workspaces/runtime/src/libraries/System.Security.Cryptography.Xml/src/System/Security/Cryptography/Xml/SignedXml.cs:line 998
   at System.Security.Cryptography.Xml.SignedXml.CheckSignature(AsymmetricAlgorithm key) in /workspaces/runtime/src/libraries/System.Security.Cryptography.Xml/src/System/Security/Cryptography/Xml/SignedXml.cs:line 283

Author:	vcsjones
Assignees:	-
Labels:	area-System.Security
Milestone:	-

[vcsjones]

My Windows box is currently sitting in pieces behind me for a few days, so waiting to see what CI says about .NET Framework before I mark as reviewable.

[bartonjs]

LGTM, provided CI agrees.

[vcsjones]

Considering the previous run was all green and the only thing that was added in the second commit is a comment, I would think the failures are unrelated.