Page has Metatag integration

Looking great already! Did a pre-emptive review 🤓

Pipeline failure is not because of the MR changes, it is a different issue. MR LGTM!

I'm concerned about applying #3487533: Cannot modify a table which uses JSON type — that's the first time XB is literally relying on a core patch. We've managed to avoid that so far.

The XB field type itself also uses JSON storage. See \Drupal\experience_builder\Plugin\Field\FieldType\ComponentTreeItem::schema().

AHHHHHH — that is literally the code that revealed that core bug! 🤯😱

But I made this use exactly the same pattern that Metatag uses, hence this bit:

* @see https://git.drupalcode.org/project/metatag/-/blob/2.0.x/src/Plugin/Field/FieldType/MetatagFieldItem.php

in \Drupal\experience_builder\Plugin\Field\FieldType\ComponentTreeItem.

So why is the Metatag module not running into the same problem? 🤔

Transplanted the relevant bits from #13 to the core bug report: #3487533-8: Cannot modify a table which uses JSON type.

This is looking great! 👏

Concerns:

1. developing XB now requires a changed setup: a core patch now is required 😬 — also not clear why the Metatag module doesn't have the same problem?! See #14.
2. the ::setProvider() magic trick that @larowlan approved needs some docs, because it is not at all obvious nor common (but neat!)
3. Default config for Metatag: how do we avoid the need for the XB module to need to provide an update path now?

Now only needs final sign-off from @tedbow WRT for this change:

-          'sqlite_type' => 'json',
+          // @todo Change back to 'json' once https://www.drupal.org/i/3487533 is resolved.
+          'sqlite_type' => 'text',

(Due to @tedbow's work on #3450957: Prevent modules from being uninstalled if they provide field types used in an Experience Builder field.)

🎉