Component slot error does not reveal the offending component

Problem/Motivation

A slots data type error throws a message like this (note the missing component):

[warning] Drupal\Core\Render\Component\Exception\InvalidComponentException: [slots.contacts] Array value found, but an object is required in Drupal\Core\Theme\Component\ComponentValidator->validateDefinition() (line 145 of /var/www/html/web/core/lib/Drupal/Core/Theme/Component/ComponentValidator.php).

Steps to reproduce

Obvious.

Proposed resolution

Add the component id to the error.

In ComponentValidator, find

    $message_parts = [
      ...$message_parts,
      ...$missing_class_errors,
    ];

Replace with:

    $message_parts = [
      sprintf('In component %s:', $definition['id']),
      ...$message_parts,
      ...$missing_class_errors,
    ];

Remaining tasks

- Roll a MR
- Review
- Commit

User interface changes

None.

Introduced terminology

None.

API changes

None.

Data model changes

None.

Release notes snippet

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