fixed locale of sub-requests when explicitely set by the developer (refs #8821)
Fixed issue #6932 - Inconsistent locale handling in subrequests

The fix consists in passing the locale in the controller reference,
inside the routablefragment renderer.
added a functional test for locale handling in sub-requests
[HttpKernel] added a comment to warn about possible inconsistencies
[Form] Fixed: submit() reacts to dynamic modifications of the form children
[Form] Removed superfluous reset() call
[Form] PropertyPathMapper::mapDataToForms() *always* calls setData() on every child to ensure
that all *_DATA events were fired when the initialization phase is over (except for virtual forms)
fixed request format when forwarding a request
[Form] Extracted ReferencingArrayIterator out of VirtualFormAwareIterator
merged branch bschussek/form-submit-2.2 (PR #8827)

This PR was merged into the 2.2 branch.

Discussion
----------

[Form][2.2] Fixed Form::submit() to react to dynamic form modifications

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

ref #3767, #3768, #4548, #8748
cc @Burgov

This PR ensures that fields that are added during the submission process of a form are submitted as well. For example:

```php
$builder = $this->createFormBuilder()
    ->add('country', 'choice', ...)
    ->getForm();

$builder->get('country')->addEventListener(FormEvents::POST_SUBMIT, function (FormEvent $event) {
    $form = $event->getForm()->getParent();
    $country = $event->getForm()->getData();

    $form->add('province', 'choice', /* ... something with $country ... */);
});
```

Currently, the field "province" will not be submitted, because the submission loop uses `foreach`, which ignores changes in the underyling array.

Additionally, this PR ensures that `setData()` is called on *every* element of a form (except those inheriting their parent data) when `setData()` is called on the root element (i.e., during initialization). Currently, when some of the intermediate nodes (e.g. embedded forms) are submitted with an empty value, `setData()` won't be called on the nodes below (i.e. the fields of the embedded form) until `get*Data()` is called on them. If `getData()` is *not* called before `createView()`, any effects of `*_DATA` event listeners attached to those fields will not be visible in the view.

Commits
-------

cd27e1f [Form] Extracted ReferencingArrayIterator out of VirtualFormAwareIterator
ccaaedf [Form] PropertyPathMapper::mapDataToForms() *always* calls setData() on every child to ensure that all *_DATA events were fired when the initialization phase is over (except for virtual forms)
19b483f [Form] Removed superfluous reset() call
00bc270 [Form] Fixed: submit() reacts to dynamic modifications of the form children
merged branch fabpot/fragment-locale (PR #8822)

This PR was merged into the 2.2 branch.

Discussion
----------

fixed locale management in sub-requests

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #6932, #5532, #8604
| License       | MIT
| Doc PR        | n/a

Same fix as #8821 but for `_locale`, and a rebase of #8604.

Commits
-------

7117328 [HttpKernel] added a comment to warn about possible inconsistencies
c4636e1 added a functional test for locale handling in sub-requests
05fdb12 Fixed issue #6932 - Inconsistent locale handling in subrequests
b3c3159 fixed locale of sub-requests when explicitely set by the developer (refs #8821)
merged branch fabpot/format-forward (PR #8829)

This PR was merged into the 2.2 branch.

Discussion
----------

fixed request format when forwarding a request

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #6932
| License       | MIT
| Doc PR        | n/a

When calling forward() in a controller, the format is not the same as for the master request.

Commits
-------

7e87eb1 fixed request format when forwarding a request
[Validator] fixed Boolean handling in XML constraint mappings (closes #5603)
merged branch fabpot/validator-xml-loader (PR #8831)

This PR was merged into the 2.2 branch.

Discussion
----------

[Validator] fixed Boolean handling in XML constraint mappings

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #5603
| License       | MIT
| Doc PR        | n/a

ping @bschussek

Commits
-------

33b0a17 [Validator] fixed Boolean handling in XML constraint mappings (closes #5603)
[Yaml] fixed embedded folded string parsing
merged branch jfsimon/issue-8472 (PR #8841)

This PR was merged into the 2.2 branch.

Discussion
----------

[Yaml] fixed embedded folded string parsing

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8779

Commits
-------

566d79c [Yaml] fixed embedded folded string parsing