Cache needs be cleared

The configuration is cached, so running assetic:dump before clearing the cache won't use the new configuration.
Update override_dir_structure.rst

Added new line to make code-block work
minor #4219 Cache needs be cleared (burki94)

This PR was submitted for the 2.5 branch but it was merged into the 2.3 branch instead (closes #4219).

Discussion
----------

Cache needs be cleared

The configuration is cached, so running assetic:dump before clearing the cache won't use the new configuration.

Commits
-------

7c2c17f Update override_dir_structure.rst
dee483f Cache needs be cleared
First draft of the bundle installation instructions
Applied all the fixes and suggestions made by reviewers
Fixed minor typo
More improvements based on reviewers' comments
Fixed some code formatting
Removed the first person perspective and other minor fixes
More tweaks and fixes
Minor fixes and tweaks
Removed the sidebar and made some minor tweaks
Reworded a bit the installation instructions
Added the fixes suggested by Ryan
feature #4236 Javiereguiluz bundle install instructions (WouterJ)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #4236).

Discussion
----------

Javiereguiluz bundle install instructions

Replaces https://github.com/symfony/symfony-docs/pull/4163

Commits
-------

7097070 Added the fixes suggested by Ryan
35dddba Reworded a bit the installation instructions
7a6644b Removed the sidebar and made some minor tweaks
41ce2a5 Minor fixes and tweaks
4b29de2 More tweaks and fixes
322ec60 Removed the first person perspective and other minor fixes
c39f7d3 Fixed some code formatting
ed96447 More improvements based on reviewers' comments
21ce2c0 Fixed minor typo
11db860 Applied all the fixes and suggestions made by reviewers
b297d29 First draft of the bundle installation instructions
Handle "constraints" option in form unit testing

In the current documentation, although a mocked `ValidatorInterface` is being passed to the `FormTypeValidatorExtension`, the actual `validate()` method in it is returning null. This causes any test against a form type that utilizes the extension's `constraints` option to fail, because of the following code in `Symfony\Component\Form\Extension\Validator\EventListener\ValidationListener`:

```php
            // Validate the form in group "Default"
            $violations = $this->validator->validate($form);

            foreach ($violations as $violation) {
                // Allow the "invalid" constraint to be put onto
                // non-synchronized forms
                $allowNonSynchronized = Form::ERR_INVALID === $violation->getCode();

                $this->violationMapper->mapViolation($violation, $form, $allowNonSynchronized);
            }
```

Note the `foreach` loop that is expecting an array.

Since the documentation uses the `ValidatorExtension` as a specific example, I think it would be nice for the example code to handle this case, preventing the user from having to dig deeper into the code to discover the problem.
Fixed return value

Replaced `array()` with `new ConstraintViolationList()`.
bug #4213 Handle "constraints" option in form unit testing (sarcher)

This PR was submitted for the 2.5 branch but it was merged into the 2.3 branch instead (closes #4213).

Discussion
----------

Handle "constraints" option in form unit testing

In the current documentation, although a mocked `ValidatorInterface` is being passed to the `FormTypeValidatorExtension`, the actual `validate()` method in it is returning null. This causes any test against a form type that utilizes the extension's `constraints` option to fail, because of the following code in `Symfony\Component\Form\Extension\Validator\EventListener\ValidationListener`:

```php
            // Validate the form in group "Default"
            $violations = $this->validator->validate($form);

            foreach ($violations as $violation) {
                // Allow the "invalid" constraint to be put onto
                // non-synchronized forms
                $allowNonSynchronized = Form::ERR_INVALID === $violation->getCode();

                $this->violationMapper->mapViolation($violation, $form, $allowNonSynchronized);
            }
```

Note the `foreach` loop that is expecting an array; currently the mocked object returns null and any test fails.

Since the documentation uses the `ValidatorExtension` as a specific example, I think it would be nice for the example code to handle this case, preventing the user from having to dig deeper into the code to discover the problem.

Commits
-------

3746f07 Fixed return value
8251e79 Handle "constraints" option in form unit testing
Merge branch '2.3' into 2.4

* 2.3:
  Fixed return value
  Handle "constraints" option in form unit testing
  Added the fixes suggested by Ryan
  Reworded a bit the installation instructions
  Removed the sidebar and made some minor tweaks
  Minor fixes and tweaks
  More tweaks and fixes
  Removed the first person perspective and other minor fixes
  Fixed some code formatting
  More improvements based on reviewers' comments
  Fixed minor typo
  Applied all the fixes and suggestions made by reviewers
  First draft of the bundle installation instructions
  Update override_dir_structure.rst
  Cache needs be cleared