[Form] Fixed: String validation groups are never interpreted as callbacks
[Form] Fixed transform()/reverseTransform() to always throw TransformationFailedExceptions
merged branch bschussek/issue7558 (PR #7917)

This PR was merged into the 2.1 branch.

Discussion
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[Form] Fixed transform()/reverseTransform() to always throw TransformationFailedExceptions

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7558
| License       | MIT
| Doc PR        | -

Commits
-------

bcb5400 [Form] Fixed transform()/reverseTransform() to always throw TransformationFailedExceptions
Merge branch '2.1' into 2.2

* 2.1:
  added additional tests to cover invalid argument exceptions in OutputFormatterStyle component
  added a missing check for the provider key
  [Validator] fixed wrong URL for XSD
  [Form] Fixed transform()/reverseTransform() to always throw TransformationFailedExceptions
  [Form] Fixed: String validation groups are never interpreted as callbacks
  if the repository method returns an array ensure that it's internal poin...
  Fix wrong method in findTaggedServiceIds(), add example to docblock.

Conflicts:
	src/Symfony/Bridge/Doctrine/Form/DataTransformer/CollectionToArrayTransformer.php
	src/Symfony/Component/Form/Extension/Core/DataTransformer/DataTransformerChain.php
	src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/ArrayToPartsTransformerTest.php
	src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/ChoiceToValueTransformerTest.php
	src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/ChoicesToValuesTransformerTest.php
	src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/DateTimeToArrayTransformerTest.php
	src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/DateTimeToRfc3339TransformerTest.php
	src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/IntegerToLocalizedStringTransformerTest.php
	src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/ValueToDuplicatesTransformerTest.php