[later phase] Comprehensive test coverage that the casted value each primitive Drupal core @DataType plugin actually does what it says

Overview

Comprehensive test coverage that the casted value each primitive Drupal core @DataType plugin actually does what it says … is sadly necessary, because 🐛 `{type: string, format: uri}` disallows image URLs containing spaces, `uri` data type stores + returns invalid URIs! Fixed revealed that this isn't true for at least \Drupal\Core\TypedData\Plugin\DataType\Uri.

Proposed resolution

• Tests, to identify what other bugs exist upstream.
• Expand src/Plugin/DataTypeOverride/*Override.php if necessary for those core bugs.

User interface changes

None.