Calling TypedConfigManager::create() does not use the definitions of TypedConfigManager (config schema), but of TypedDataManager (field types)

Problem/Motivation

Discovered in #3364108: Configuration schema & required keys.

TypedConfigManager does not correctly override all of the methods of its base class, TypedDataManager.

The result is that sometimes it will get confused and NOT use the correct plugin definitions (*.schema.yml files' contents, surfaced by \Drupal\Core\Config\Schema\ConfigSchemaDiscovery), but instead those of the parent class (@DataType plugins).

Steps to reproduce

Proposed resolution

Add the test coverage that was overlooked in #1866610: Introduce Kwalify-inspired schema format for configuration.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet