fix:this->error can be reset in the middle of validateOrThrow

[jwadhams]

Caught a problem in production where some times validateOrThrow will throw a type error

"Carsdotcom\\JsonSchemaValidation\\Exceptions\\JsonSchemaValidationException::__construct(): Argument #2 ($error) must be of type Opis\\JsonSchema\\Errors\\ValidationError, null given, called in /var/www/html/vendor/carsdotcom/laravel-json-schema/app/SchemaValidatorService.php on line 141"

I wasn't able to reproduce the problem in a unit test (even using an exact copy of this DealData and an export-import of the Account). I ended up copy-pasting the implementation of validateOrThrow into Tinker on the affected Kubernetes pod, where I was able to reproduce, and experimenting with echo statements and iteratively rewriting.

The problem appears to be that in a complicated app, the Log::debug call can synchronously involve other systems, some of which may also be using this Facade to validate other data. In some roundabout way Log::debug is causing SchemaValidatorService::error to be reset to null -- because SchemaValidatorProvider is intentionally designed to be a singleton that $error property is effectively a global. Yikes!

The fix in Tinker was to get error into a local variable at the top of the method. But I think the right fix for the library is to obsolete the pattern where validate returns a boolean, then the race is on to get the error -- instead I introduced a method that returns the full \Opis\JsonSchema\ValidationResult (both boolean valid plus the errors array, in one bundle) and refactored validateOrThrow to use that method. I also totally obsoleted the idea of getting the error in a separate call, since as a singleton that can't ever be totally safe.

[jwadhams]

Note to Cars.com team, you can test this in Online Shopper before we merge by editing composer.json like

        "carsdotcom/laravel-json-schema": "dev-hotfix/error-disappears-during-reporting as 1.0.2",

then running

composer upgrade carsdotcom/laravel-json-schema

(You have to use the as syntax or it won't understand how this fulfills the requirements for JsonModel)