Fix yoast breadcrumbs front

[herrvigg]

From #1077 by @Komarovski

Hello everyone, I've made some frontend fixes for Yoast SEO module that prevent outputting wrong language data in breadcrumbs from indexable tables and also added filters for schema, opengraph and next|prev links.

Tested on: Wordpress version: 5.8.1 qTranslate XT version: 3.11.0 Yoast SEO version: 17.4

[herrvigg]

A few questions

[herrvigg]

Pushed a few fixes. I don't use these features myself so I trust you. I think we can merge this.

[herrvigg]

Merged in master so more people can test. If you spot new errors let us know.

[herrvigg]

Perhaps we should keep your comments somewhere in the wiki, the first part fort he indexation might be useful for the users:

Use indexation only in backend on "publish/update" events to save all languages data in indexable tables.
If you allow indexation on the frontend - then indexable table will save data of the first visited page, all other languages data will be missed/filtered/gone/didn't saved.
After all this fixes everyone need to install "Yoast Test Helper", go to "Instruments -> Yoast Test" and reset "Indexables & migrations table", then go to "SEO -> Instruments" and start SEO data optimization.
This filters "wpseo_should_save_indexable", "wpseo_indexing_data" - right now works only on frontend, so using of "!is_admin()" is pointless, but maybe in future this filters will work on backend, that's why I have leaved "!is_admin()" below.
Unfortunately I didn't found how to totally disable indexable feature, Yoast documentation is very poor to quickly understand how everything works.
Also be advised that after Yoast have added indexables - now you also need to provide breadcrumb titles and its translations even if they are same as in title. If you wouldn't provide breadcrumb title & translation - Yoast will only index current language title.

[herrvigg]

After all this fixes everyone need to install "Yoast Test Helper",

@Komarovski what is the impact if we don't do so?

[Komarovski]

After all this fixes everyone need to install "Yoast Test Helper",

@Komarovski what is the impact if we don't do so?

If don't do so - Yoast SEO will use old data from indexables table that could not have all translations in titles, descriptions, breadcrumbs.
Other way to update indexables table so it could store all translated content without using Yoast Test Helper - is manually update all posts, pages, custom post types items, categories, tags, custom taxonomy terms, author pages.

After updating to qTranslate-XT 3.11.1 version - this operation needs to be done one time.