… into UUIDs (webmozart)This PR was merged into the 2.8 branch.Discussion----------[Validator] Added missing error codes and turned codes into UUIDsReopened#12388 on the 2.8 branch.| Q             | A| ------------- | ---| Bug fix?      | no| New feature?  | no| BC breaks?    | no| Deprecations? | no| Tests pass?   | yes| Fixed tickets | -| License       | MIT| Doc PR        | -With the current implementation of error codes, checking which error occurred is unnecessarily complex:```phpif ($violation->getConstraint() instanceof Length && Length::TOO_SHORT_ERROR === $violation->getCode()) {    // ...}```Also, the code is completely missing for some constraints. This is fixed now. By using UUIDs, the check is reduced to:```phpif (Length::TOO_SHORT_ERROR === $violation->getCode()) {    // ...}```Also, APIs can simply output the error code and the name of the error without needing to point to the constraint as well.Before:```json[    {        "code": "1",        "name": "TOO_SHORT_ERROR",        "message": "This value is too short. ...",        "constraint": "Symfony\\Component\\Validator\\Constraints\\Length"    }]```After:```json[    {        "code": "9ff3fdc4-b214-49db-8718-39c315e33d45",        "name": "TOO_SHORT_ERROR",        "message": "This value is too short. ..."    }]```This makes it possible to implement a service on symfony.com which looks up error codes, e.g.symfony.com/error?code=9ff3fdc4-b214-49db-8718-39c315e33d45Such a URL could redirect directly to the documentation of the appropriate constraint. We could even support user-submitted error codes which redirect to the documentation of that constraint.Commits-------8874e88 [Validator] Added missing error codes and turned codes into UUIDs

…(Koc)This PR was merged into the 2.8 branch.Discussion----------[DoctrineBridge] added missing error code for constraint.| Q             | A| ------------- | ---| Branch?       | 2.8| Bug fix?      | yes| New feature?  | no| BC breaks?    | no| Deprecations? | no| Tests pass?   | wait for travis| Fixed tickets |#15154| License       | MIT| Doc PR        | -Commits-------32cb269 [DoctrineBridge] added missing error code for constraint.

…straint fails. (Koc)This PR was merged into the 3.3-dev branch.Discussion----------[DX][Form][Validator] Add ability check if cocrete constraint fails.| Q | A || --- | --- || Branch? | master || Bug fix? | no || New feature? | yes || BC breaks? | no || Deprecations? | no || Tests pass? | wait for travis || Fixed tickets |#15154 || License | MIT || Doc PR | should open |Sometimes for big forms with multiple constraints we should handle some errors separately.``` php// when using validator$constraintViolations = $validator->validate(...);if (count($constraintViolations->findByCodes(UniqueEntity::NOT_UNIQUE_ERROR))) {  // display some message or send email or etc}// when using formsif (count($form->getErrors()->findByCodes(UniqueEntity::NOT_UNIQUE_ERROR))) {  // display some message or send email or etc}```This PR add some useful methods to handle this. Before we should iterate all failed constraints using foreach.Feel free to suggest better names for new methods.Commits-------29a3a7e Add ability retrieve errors by their code.