[Core] Add authorization challenge parsing helper

[mccoyp]

Description

Resolves #23613. This is a follow-up to #24019, adjusting to feedback in Azure/azure-sdk#4302. Instead of adding a new policy to handle authorization challenges, this PR follows other languages' lead in providing a helper class for parsing challenges (see .NET's), and leaves the implementation of on_challenge and/or custom on_request methods to BearerTokenCredentialPolicy subclasses.

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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Testing Guidelines

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[azure-sdk]

API change check

APIView has identified API level changes in this PR and created following API reviews.

azure-core

[ghost]

Hi @mccoyp. Thank you for your interest in helping to improve the Azure SDK experience and for your contribution. We've noticed that there hasn't been recent engagement on this pull request. If this is still an active work stream, please let us know by pushing some changes or leaving a comment. Otherwise, we'll close this out in 7 days.

[ghost]

Hi @mccoyp. Thank you for your contribution. Since there hasn't been recent engagement, we're going to close this out. Feel free to respond with a comment containing "/reopen" if you'd like to continue working on these changes. Please be sure to use the command to reopen or remove the "no-recent-activity" label; otherwise, this is likely to be closed again with the next cleanup pass.