Added missing files .gitignore
Merge branch '2.3'

* 2.3:
  [Validator] fixed ConstraintViolation:: incorrect when nested
  handle Optional and Required constraints from XML or YAML sources correctly
  added missing comments to WebTestCase
  Fixed #8455: PhpExecutableFinder::find() does not always return the correct binary
  Added missing files .gitignore
  [DependencyInjection] Fix Container::camelize to convert beginning and ending chars
  [Validator] Fixed groups argument misplace for validateValue method from validator class
  [Form] Fix of "PATCH'ed forms are never valid"