[Form][Validator] All index items after children are to be considered grand-children when resolving ViolationPath (fixes #11458)
[Translation] made XliffFileDumper support CDATA sections.
[FrameworkBundle] Add Event Dispatcher debug command
[Form] FormBuilder::getIterator() now deals with resolved children
[Twig][Form] Moved configuration key twig.form.resources to
twig.form_themes
fix handling of empty sequence items

When a line contains only a dash it cannot safely be assumed that
it contains a nested list or an embedded mapping. If the next line
starts with a dash at the same indentation, the current line's item
is to be treated as `null`.
[Monolog] added NotFoundActivationStrategy from MonologBundle
make the stopwatch service always available

Previously, one had to be careful to check if the debug.stopwatch
service was available before using it. Otherwise, the application
would break in the prod environment.
[DI] Added safeguards against invalid config in the YamlFileLoader

Exceptions explaining the mistake are better than fatal errors or weird
notices appearing when trying to deal with such invalid data.
Closes #11333
updated CHANGELOG for 2.3.19
update CONTRIBUTORS for 2.3.19
updated VERSION for 2.3.19
updated CHANGELOG for 2.4.9
updated VERSION for 2.4.9
updated CHANGELOG for 2.5.4
updated VERSION for 2.5.4
bumped Symfony version to 2.3.20
bumped Symfony version to 2.4.10
bumped Symfony version to 2.5.5
improve error when detecting unquoted asterisks

Asterisks in unquoted strings are used in YAML to reference
variables. Before Symfony 2.3.19, Symfony 2.4.9 and Symfony 2.5.4,
unquoted asterisks in inlined YAML code were treated as regular
strings. This was fixed for the inline parser in #11677. However, an
unquoted * character now led to an error message like this:

```
PHP Warning:  array_key_exists(): The first argument should be either a string or an integer in vendor/symfony/symfony/src/Symfony/Component/Yaml/Inline.php on line 409

  [Symfony\Component\Yaml\Exception\ParseException]
  Reference "" does not exist at line 171 (near "- { foo: * }").
```