feat: add migration validation of converted data

[larskemper]

resolves #11813

covered validation:

• missing required fields
• unexpected fields
• validation of field value
• lookup of foreign key mapping

[jozsefdamokos]

LGTM so far

[ennasus4sun]

looks good to me, too.
just one thought:

[Copilot]

Pull Request Overview

This PR implements migration validation of converted data to ensure data integrity during migration processes. It introduces comprehensive validation logic that checks entity structure, field values, and foreign key relationships.

• Validates missing required fields, unexpected fields, and field value constraints
• Validates foreign key mappings to ensure referential integrity
• Provides extensible event-driven validation framework with pre/post validation events

Reviewed Changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/Migration/Validation/SwagMigrationValidationService.php	Core validation service implementing structure, field, and association validation logic
src/Migration/Validation/SwagMigrationValidationContext.php	Context object holding validation state and converted data
src/Migration/Validation/SwagMigrationValidationResult.php	Result container for validation logs and entity information
src/Migration/Validation/Log/	Validation-specific log classes for different error types
src/Migration/Validation/Event/	Pre and post validation events for extensibility
src/Migration/Service/MigrationDataConverter.php	Integration of validation service into data conversion process
src/Migration/Mapping/MappingService.php	Added foreign key validation method
tests/	Comprehensive test coverage for all validation components

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}