Add @api annotation to Filter Group & Sort Order

[navarr]

Description

This PR adds the FilterGroup and SortOrder classes to the public API for the magento/framework component. They are the only pieces of SearchCriteriaInterface that are not identified with an @api annotation. This causes usages of them for searching repositories in modules to depend on the patch level of the framework. Once merged, modules may use them while depending on the major version of the framework.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-cicd2]

All committers have signed the CLA.

[magento-engcom-team]

Hi @navarr. Thank you for your contribution
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[magento-engcom-team]

Hi @navarr. Thank you for your contribution.
We will aim to release these changes as part of 2.3.0.
Please check the release notes for final confirmation.