feat: add support for .NET SDK V4

[philasmar]

Issue #, if available:
DOTNET-7759

Description of changes:

• Added .NET 8 target framework and marked as trimmable
• Updated the .NET SDK dependencies to the latest version 4.0.0-preview.4
• Add SourceLink support

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[normj]

Nevermind this comment. Posted on the wrong PR.

[normj]

The GetUserPoolClientConfiguration method in CognitoUserPool is passing in collections into CognitoUserPoolClientConfiguration which doesn't accept nulls. We should probably pass in empty collections if the the DescribeUserPoolClientAsync returns back null collection.

I'm pretty sure the AuthParameters at this point should not be null but I would still add a defensive check: https://github.com/aws/aws-sdk-net-extensions-cognito/blob/master/src/Amazon.Extensions.CognitoAuthentication/CognitoUserAuthentication.cs#L76C33-L76C47

The null checks for the challengeParameters don't look complete in this method. UpdateUsernameAndSecretHash

Make sure the ChallengeResponses property is not null at this point: https://github.com/aws/aws-sdk-net-extensions-cognito/blob/master/src/Amazon.Extensions.CognitoAuthentication/CognitoUserAuthentication.cs#L96

The ChallengeParameters parameter needs some null checking: https://github.com/aws/aws-sdk-net-extensions-cognito/blob/master/src/Amazon.Extensions.CognitoAuthentication/CognitoUserAuthentication.cs#L175

Add some null checks on these collections. I'm not exactly sure where these collections are coming from but it might be from service responses.
https://github.com/aws/aws-sdk-net-extensions-cognito/blob/master/src/Amazon.Extensions.CognitoAuthentication/CognitoUser.cs#L774
https://github.com/aws/aws-sdk-net-extensions-cognito/blob/master/src/Amazon.Extensions.CognitoAuthentication/CognitoUser.cs#L792
https://github.com/aws/aws-sdk-net-extensions-cognito/blob/master/src/Amazon.Extensions.CognitoAuthentication/Util/CognitoAuthHelper.cs#L129
https://github.com/aws/aws-sdk-net-extensions-cognito/blob/master/src/Amazon.Extensions.CognitoAuthentication/CognitoDevice.cs#L317

[philasmar]

The GetUserPoolClientConfiguration method in CognitoUserPool is passing in collections into CognitoUserPoolClientConfiguration which doesn't accept nulls. We should probably pass in empty collections if the the DescribeUserPoolClientAsync returns back null collection.

I'm pretty sure the AuthParameters at this point should not be null but I would still add a defensive check: https://github.com/aws/aws-sdk-net-extensions-cognito/blob/master/src/Amazon.Extensions.CognitoAuthentication/CognitoUserAuthentication.cs#L76C33-L76C47

The null checks for the challengeParameters don't look complete in this method. UpdateUsernameAndSecretHash

Make sure the ChallengeResponses property is not null at this point: https://github.com/aws/aws-sdk-net-extensions-cognito/blob/master/src/Amazon.Extensions.CognitoAuthentication/CognitoUserAuthentication.cs#L96

The ChallengeParameters parameter needs some null checking: https://github.com/aws/aws-sdk-net-extensions-cognito/blob/master/src/Amazon.Extensions.CognitoAuthentication/CognitoUserAuthentication.cs#L175

Add some null checks on these collections. I'm not exactly sure where these collections are coming from but it might be from service responses. https://github.com/aws/aws-sdk-net-extensions-cognito/blob/master/src/Amazon.Extensions.CognitoAuthentication/CognitoUser.cs#L774 https://github.com/aws/aws-sdk-net-extensions-cognito/blob/master/src/Amazon.Extensions.CognitoAuthentication/CognitoUser.cs#L792 https://github.com/aws/aws-sdk-net-extensions-cognito/blob/master/src/Amazon.Extensions.CognitoAuthentication/Util/CognitoAuthHelper.cs#L129 https://github.com/aws/aws-sdk-net-extensions-cognito/blob/master/src/Amazon.Extensions.CognitoAuthentication/CognitoDevice.cs#L317

I went through the code base and added more defensive checks for collections.