Inappropriate error detail for UniqueEntity annotation error

### Bug Report

| Q | A
|------------ | ------
| BC Break | No
| Version | All

#### Summary

I found an error trying to validate the doctrine schema:

```
php bin/console doctrine:schema:validate --verbose

Mapping
-------

In Constraint.php line 163:

[Symfony\Component\Validator\Exception\MissingOptionsException]
The options "fields" must be set for constraint "Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity".

Exception trace:
at F:\websites\crayner\quoll\vendor\symfony\validator\Constraint.php:163
Symfony\Component\Validator\Constraint->normalizeOptions() at F:\websites\crayner\quoll\vendor\symfony\validator\Constraint.php:108
Symfony\Component\Validator\Constraint->__construct() at F:\websites\crayner\quoll\vendor\doctrine\annotations\lib\Doctrine\Common\Annotations\DocParser.php:827
Doctrine\Common\Annotations\DocParser->Annotation() at F:\websites\crayner\quoll\vendor\doctrine\annotations\lib\Doctrine\Common\Annotations\DocParser.php:662
Doctrine\Common\Annotations\DocParser->Annotations() at F:\websites\crayner\quoll\vendor\doctrine\annotations\lib\Doctrine\Common\Annotations\DocParser.php:354
Doctrine\Common\Annotations\DocParser->parse() at F:\websites\crayner\quoll\vendor\doctrine\annotations\lib\Doctrine\Common\Annotations\AnnotationReader.php:221
Doctrine\Common\Annotations\AnnotationReader->getClassAnnotations() at F:\websites\crayner\quoll\vendor\doctrine\annotations\lib\Doctrine\Common\Annotations\CachedReader.php:80
Doctrine\Common\Annotations\CachedReader->getClassAnnotations() at F:\websites\crayner\quoll\vendor\doctrine\persistence\lib\Doctrine\Persistence\Mapping\Driver\AnnotationDriver.php:177
Doctrine\Persistence\Mapping\Driver\AnnotationDriver->isTransient() at F:\websites\crayner\quoll\vendor\doctrine\persistence\lib\Doctrine\Persistence\Mapping\Driver\AnnotationDriver.php:245
Doctrine\Persistence\Mapping\Driver\AnnotationDriver->getAllClassNames() at F:\websites\crayner\quoll\vendor\doctrine\persistence\lib\Doctrine\Persistence\Mapping\Driver\MappingDriverChain.php:107
Doctrine\Persistence\Mapping\Driver\MappingDriverChain->getAllClassNames() at F:\websites\crayner\quoll\vendor\doctrine\persistence\lib\Doctrine\Persistence\Mapping\AbstractClassMetadataFactory.php:90
Doctrine\Persistence\Mapping\AbstractClassMetadataFactory->getAllMetadata() at F:\websites\crayner\quoll\vendor\doctrine\orm\lib\Doctrine\ORM\Tools\SchemaValidator.php:68
Doctrine\ORM\Tools\SchemaValidator->validateMapping() at F:\websites\crayner\quoll\vendor\doctrine\orm\lib\Doctrine\ORM\Tools\Console\Command\ValidateSchemaCommand.php:69
Doctrine\ORM\Tools\Console\Command\ValidateSchemaCommand->execute() at F:\websites\crayner\quoll\vendor\doctrine\doctrine-bundle\Command\Proxy\ValidateSchemaCommand.php:34
Doctrine\Bundle\DoctrineBundle\Command\Proxy\ValidateSchemaCommand->execute() at F:\websites\crayner\quoll\vendor\symfony\console\Command\Command.php:258
Symfony\Component\Console\Command\Command->run() at F:\websites\crayner\quoll\vendor\symfony\console\Application.php:929
Symfony\Component\Console\Application->doRunCommand() at F:\websites\crayner\quoll\vendor\symfony\framework-bundle\Console\Application.php:96
Symfony\Bundle\FrameworkBundle\Console\Application->doRunCommand() at F:\websites\crayner\quoll\vendor\symfony\console\Application.php:264
Symfony\Component\Console\Application->doRun() at F:\websites\crayner\quoll\vendor\symfony\framework-bundle\Console\Application.php:82
Symfony\Bundle\FrameworkBundle\Console\Application->doRun() at F:\websites\crayner\quoll\vendor\symfony\console\Application.php:140
Symfony\Component\Console\Application->run() at F:\websites\crayner\quoll\bin\console:42
```

The issue here is not with the error, but in the fact that the error is not correctly identifying the issue, which is a annotation parse error, causing the Contraint violation. Unfortunately, this error does not identify the entity at fault, and I had to remove ALL UniqueEntity references in 150+ entities and return them one at a time to eventually find the error. The error on the annotation looks like:

```
...
use Doctrine\ORM\Mapping as ORM;
use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity;
...

* @ORM\Table(name="Scale",
* indexes={@ORM\Index(name="lowest_acceptable",columns={"lowest_acceptable"})},
* uniqueConstraints={@ORM\UniqueConstraint(name="name",columns={"name"}),
* @ORM\UniqueConstraint(name="abbreviation",columns={"abbreviation"}),
* })
* @UniqueEntity{"name"})
* @UniqueEntity({"abbreviation"})

```

The error is on the "name" line, which is missing the opening bracket.

#### Current behavior

The current behaviour is as stated above.

#### How to reproduce

Remove the opening bracket on any UniqueEntity annotation will duplicate this issue.

#### Expected behavior

```
[Doctrine\Common\Annotations\AnnotationException]
[Syntax Error] Failed to see bracket set at position xxx in class App\Entity\Name.
```