Add Compile-time annotation-processor tool to clientcore

[samvaity]

Description

Creates a new /sdk/clientcore/tools package named annotation-processor, which serves as a shippable replacement for the in-house RestProxy annotation processing utilities used to generate HTTP client service implementations.

This package addresses common challenges with service client implementations relying on the intermediate RestProxy layer, which introduces reflection-based inefficiencies, negatively impacts performance, and produces less readable stack traces. Instead, annotation-processor uses JavaPoet to process annotations and generate service client implementations. Currently, it generates the respective service client implementation in ${project.build.directory}/generated-sources/.

Remaining Work:

• Enhance response body handling to manage complex cases.
• Address minor issues in public API generation.
• Generate comprehensive Javadocs for generated code.

This implementation currently supports end-to-end functionality for the OpenAI getChatCompletions API as a proof of concept.

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.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[alzimmermsft]

Approving even though further review could be done as unblocking this to begin generating SDKs with this is more important and will find more issues than code review.