Support Pods fields in REST API as params for meta query

[JoryHogeveen]

Description

This PR will add basic support for meta based REST API queries when passing Pods fields as parameters.

Related GitHub issue(s)

Fixes #7210

Testing instructions

1. Create CPT (or use Post)
2. Add a custom field
3. Enable REST API
4. Query field: example.com/wp-json/wp/v2/{CPT}?{FIELDNAME}={VALUE}

Changelog text for these changes

PR checklist

• [x] I have tested my own code to confirm it works as I intended.
• [x] My code follows the WordPress Coding Standards.
• [x] My code follows the WordPress Inline Documentation Standards.
• [ ] My code includes automated tests for PHP and/or JS (if applicable).