[Form][Validator] All index items after children are to be considered grand-children when resolving ViolationPath (fixes #11458)
[Translation] made XliffFileDumper support CDATA sections.
[Form] FormBuilder::getIterator() now deals with resolved children
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`.
[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: * }").
```
improve handling router script paths

The `server:run` command switches the working directory before
starting the built-in web server. Therefore, the path to a custom
router script had to be specified based on the document root path
and not based on the user's working directory.
Escape parameter on generated response
add missing exceptions to docblock
bug #11843 [Yaml] improve error message when detecting unquoted asterisks (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
----------

[Yaml] improve error message when detecting unquoted asterisks

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11835
| License       | MIT
| Doc PR        |

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: * }").
```

Commits
-------

854e07b improve error when detecting unquoted asterisks