* Property level validation for content - initial implementation
* Always succeed create/update regardless of property level validation errors
* Move old complex editor validation classes to Web.BackOffice so they will be deleted
* Include operation status and property validation errors in ProblemDetails
* Refactor property validation to its own service(s)
* Make the problem details builder a little more generic towards extensions
* Validation for item and branch publish
* Moved malplaced test
* Get rid of a TODO
* Integration tests for content validation service
* Simplify validation service
* Add missing response types to create and update for document and media
* Remove test that no longer applies
* Use "errors" for model validation errors (property validation errors)
* Split create/update and validation into their own endpoints
* Fix forward merge
* Correct wrong assumption for missing properties
* Remove localization from validation error messages - decreases dependencies, adds a lot of obsolete constructors
* Reuse existing validation service + support custom error messages
* Fix merge errors
* Review comments
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