Revert the creation of Smithy.Identity.Abstractions project and move its interfaces to AWSSDK.Core

[muhammad-othman]

Description

• Removed Smithy.Identity.Abstractions project and update its references to use AWSSDK.Core instead.
• Moved Smithy.Identity.Abstractions interfaces to AWSSDK.Core
• Moved DefaultAWSCredentialsIdentityResolver, DefaultAWSCredentialsIdentityResolver and AnonymousIdentityResolver from internal namespace to Amazon.Runtime.
• Included the generated changes for AutoScaling and S3 only to keep the PR small.

Motivation and Context

• DOTNET-7844

Testing

• DRY_RUN-6c97e06c-7f6b-480b-98b0-9cc2369be5c0

[normj]

For these new types have the namespace match the folder structure. So in this case the namespace is Amazon.Runtime.Auth. I know the types in the Credentials folder use the Amazon.Runtime namespace instead of Amazon.Runtime.Credentials but all of the other subnamespaces don't follow that pattern. I can remember why we are inconsistent with Credentials but we should not overload the Amazon.Runtime namespace`.

The other question are we comfortable with these interfaces being "public" to users or should we put them in Amazon.Runtime.Internal.Auth for now? I'm concern we still haven't defined the ISigner interface with it having a big TODO. We have more flexibility if we start with Amazon.Runtime.Internal.Auth.

[muhammad-othman]

I was trying to follow the same pattern that we used for the credentials, didn't know that it is the exception. Will update it in the next revision.

The reason I made these interfaces public is that some of them are needed for public configurations like ClientConfig.AWSTokenProvider & ClientConfig.IdentityResolverConfiguration or they types of these configurations properties. ISigner would be an exception to this since it is used by the IAuthScheme which shouldn't be created by the users.
What do you think about only moving ISigner&IAuthScheme to an internal namespace since these are the only ones that we don't expect the users to interact with?

[normj]

If ISigner and IAuthScheme do need to be accessed by users I would move them to the internal namespace. Especially since currently are signers are in the internal namespace. We could potentially move the later when/if we decided to separate signers which is a customer ask.