Migrate Identity libraries to new linting format

[alzimmermsft]

Description

Migrates the Identity libraries to the new linting format where each library defines their own Checkstyle and Spotbugs suppressions, rather than relying on the global suppressions which are both less direct for each library and can result in inadvertent suppression.

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.

[azure-sdk]

API change check

API changes are not detected in this pull request.

[billwert]

looks good for Identity changes.