feat(core): Update all references to use new auth class using flare identity server for Amazon Q

[opieter-aws]

Problem

The business logic of auth-related features is complex and implemented separately for all IDEs. Flare/DEXP LSP server has implemented auth that can be reused for all IDEs. The source code was introduced already introduced in #6958 with activation and client updates in #7062. But the references to AuthUtil through the codebase weren't updated yet.

Solution

• Update all remaining references to AuthUtil in the codebase
• All toolkits unit tests are passing
• Disable telemetry and existing AuthUtil unit tests, to be updated in follow-up PR
• amazonq and web unit tests still failing, to be addressed in follow-up PR

Note that CI is expected to fail for amazonq and web unit tests

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• Treat all work as PUBLIC. Private feature/x branches will not be squash-merged at release time.
• Your code changes must meet the guidelines in CONTRIBUTING.md.
• License: I confirm that my contribution is made under the terms of the Apache 2.0 license.

[github-actions]

• This pull request implements a feat or fix, so it must include a changelog entry (unless the fix is for an unreleased feature). Review the changelog guidelines.
  • Note: beta or "experiment" features that have active users should announce fixes in the changelog.
  • If this is not a feature or fix, use an appropriate type from the title guidelines. For example, telemetry-only changes should use the telemetry type.