Extract Audience_Utilities from Analytics_4.

[arkaitzbitorika]

Summary

Addresses issue:

• Extract the audience utility logic from Analytics_4 to a new class. #9229

Relevant technical choices

• Created Audience_Utilities with audience-related code from Analytics_4.
• Created Audience_UtilitiesTest with unittests for Audience_Utilities.
• Removed audience related code from Analytics_4 and made it use Audience_Utilities instead.

PR Author Checklist

• [x ] My code is tested and passes existing unit tests.
• [ x] My code has an appropriate set of unit tests which all pass.
• [ x] My code is backward-compatible with WordPress 5.2 and PHP 7.4.
• My code follows the WordPress coding standards.
• [x ] My code has proper inline documentation.
• I have added a QA Brief on the issue linked above.
• [x ] I have signed the Contributor License Agreement (see https://cla.developers.google.com/).

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Code Reviewer Checklist

• Run the code.
• Ensure the acceptance criteria are satisfied.
• Reassess the implementation with the IB.
• Ensure no unrelated changes are included.
• Ensure CI checks pass.
• Check Storybook where applicable.
• Ensure there is a QA Brief.
• Ensure there are no unexpected significant changes to file sizes.

Merge Reviewer Checklist

• Ensure the PR has the correct target branch.
• Double-check that the PR is okay to be merged.
• Ensure the corresponding issue has a ZenHub release assigned.
• Add a changelog message to the issue.

[github-actions]

Build files for 847f433 have been deleted.

[arkaitzbitorika]

Verified that the failing E2E tests pass in my local environment.

[eugene-manuilov]

LGTM