Fatal InvalidArgumentException on filter format save after CKEditor 5 migration

Saving a filter format that includes the Markdown filter throws two fatals on sites that went through a CKEditor 5 migration:

1. InvalidArgumentException: The configuration property id doesn't exist in ValidKeysConstraintValidator::getDynamicMessageParameters() — the extension settings array lacks an id key, so the dynamic schema type markdown.extension_settings.[%parent.id] cannot resolve.
2. InvalidArgumentException in BaseExtension::validateSettings() — same missing id causes Mapping::get('id') to throw.

The root cause: the CKEditor 5 migration leaves a stale id: filter_null entry in the filter format config, which is later removed during a config import. Without it, extension data submitted by the form is keyed by extension ID rather than containing an id property, breaking schema resolution.

Fix (attached patch):

• ParserConfigurationForm.php: inject the extension ID as a #type => 'value' element so submitted data always contains id; add #input => FALSE to the experimental notice element to prevent it from submitting a spurious experimental key.
• BaseExtension.php: catch InvalidArgumentException from Mapping::get('id') and skip validation gracefully.
• markdown.schema.yml: declare vertical_tabs: type: ignore (form widget submits an __active_tab value into this namespace); add missing markdown.extension_settings.commonmark-footnotes schema; add missing constraints to the Table of Contents style key.