Rework low-level HTTP methods and Response structure

[alzimmermsft]

Description

This PR is overhauling low-level design concepts with HttpClient.send, HttpPipeline.send, and associated policy classes to explicitly return Response<BinaryData> rather than Response<?> and removed HttpResponse and makes Response a class instead of an interface.

The reasoning behind this change is the pattern for handling conversion of the raw network response to the SDK Response<T> was forcing the use of HttpResponse and HttpResponseAccessHelper from outside libraries, and that Response vs HttpResponse caused confusion on which should be used. This simplifies the story to be:

1. Any interactions at or near the networking layer strictly work with BinaryData.
2. When we're switching from the networking layer to SDK layer we take the raw BinaryData payload and convert it to T.

This removes the need for hidden deserialization and exposing implementation packages outside of ClientCore.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

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• Pull request includes test coverage for the included changes.

[azure-sdk]

API change check

API changes are not detected in this pull request.