Pods 2.8 i18n integration classes

[JoryHogeveen]

Description

This PR moved all i18n compatibility for third party plugins (WPML and Polylang) to dedicated integration classes.

Related GitHub issue(s)

Related: #5029

Tasklist

• Call integration classes hook() methods to activate them
• Test refactor Polylang (Jory)
• Test refactor WPML (Jory)
• Test refactor (others)
• Confirm API usage (Polylang)
• Confirm API usage (WPML)
• Fix [Pods 2.8 Bug] testing on site using WPML gives error #5945
• Fix Update and fix WPML integration + enhance i18n compatibility in general #5968

Testing instructions

1. Install a translator (Polylang / WPML)
2. Create at least two languages
3. Add relationship fields for posts and taxonomies (type doesn't matter)
4. Add posts and taxonomies for both languages (at least 3 and make sure the language locale is in the title so you can easily verify it works
5. Check the options in the relationship fields. Only relationships of the SAME language should be available.
6. Also check the shortcodes (query). If you query Pods from a page then the query should only return objects of the same language. Shortcode example: [pods name="test"]{@title} [/pods]
7. Check if more complex shortcodes (with where statements etc.) keep working correctly.

Changelog text for these changes

PR checklist

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

[sc0ttkclark]

@JoryHogeveen is #5945 confirmed resolved by this now?

We can go ahead and merge this ahead of the WPML call too, it's a major improvement

[JoryHogeveen]

@sc0ttkclark
I'm not sure if #5945 is 100% resolved in this PR but I doub't remaining issues are actually related to this PR.
I do believe that this PR makes sure there are not query errors relating to WPML integration anymore so that part is fixed.