[Form] Check if IntlDateFormatter constructor returned a valid object before using it
[Process] Reduce I/O load on Windows platform
[Translator][FrameworkBundle] Added @ to the list of allowed chars in Translator
bug #11403 [Translator][FrameworkBundle] Added @ to the list of allowed chars in Translator (takeit)

This PR was squashed before being merged into the 2.3 branch (closes #11403).

Discussion
----------

[Translator][FrameworkBundle] Added @ to the list of allowed chars in Translator

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11396
| License       | MIT

Commits
-------

3176f8b [Translator][FrameworkBundle] Added @ to the list of allowed chars in Translator
[Validator] Backported #11410 to 2.3: Object initializers are called only once per object
bug #11411 [Validator] Backported #11410 to 2.3: Object initializers are called only once per object (webmozart)

This PR was merged into the 2.3 branch.

Discussion
----------

[Validator] Backported #11410 to 2.3: Object initializers are called only once per object

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

Before, object initializers were called multiple times if an object was validated in different groups in the same validation run. The initializers, however, are not aware of the current validation group, so calling them more than once does not make sense.

Now, object initializers are called exactly once per validated object.

See #11410

Commits
-------

291cbf9 [Validator] Backported #11410 to 2.3: Object initializers are called only once per object
Optimize assertLocale regexp
minor #11441 [Translator] Optimize assertLocale regexp (Jérémy Derussé)

This PR was merged into the 2.3 branch.

Discussion
----------

[Translator] Optimize assertLocale regexp

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

Optimize regexp by remove unused variable and using anchored regex.
Thanks @Tobion

Commits
-------

537c39b Optimize assertLocale regexp
bug #11342 [2.3][Form] Check if IntlDateFormatter constructor returned a valid object before using it (romainneutron)

This PR was merged into the 2.3 branch.

Discussion
----------

[2.3][Form] Check if IntlDateFormatter constructor returned a valid object before using it

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

`IntlDateFormatter` constructor [may return false](http://www.php.net/manual/en/intldateformatter.create.php#refsect1-intldateformatter.create-returnvalues). This patches avoids fatal errors in these cases

This PR replaces #11334

Commits
-------

ebf967d [Form] Check if IntlDateFormatter constructor returned a valid object before using it
bug #11120 [2.3][Process] Reduce I/O load on Windows platform (romainneutron)

This PR was merged into the 2.3 branch.

Discussion
----------

[2.3][Process] Reduce I/O load on Windows platform

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

When using file handles, no `stream_select` call is done.
On linux platforms, `stream_select` introduce a sleep as it has 0.2s timeout, there is no such pause on Windows, producing lot's of disk I/Os when reading file handles

Commits
-------

ff0bb01 [Process] Reduce I/O load on Windows platform
[Translator] Use quote to surround invalid locale
minor #11464 [Translator] Use quote to surround invalid locale (lyrixx)

This PR was submitted for the 2.5 branch but it was merged into the 2.3 branch instead (closes #11464).

Discussion
----------

[Translator] Use quote to surround invalid locale

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

I got this message in one application (CLI):

```

  [InvalidArgumentException]
  Invalid locale: en_US .

```

It's not so easy to spot the issue.

Commits
-------

c9742ef [Translator] Use quote to surround invalid locale
Merge branch '2.3' into 2.4

* 2.3:
  [Translator] Use quote to surround invalid locale
  Optimize assertLocale regexp
  [Validator] Backported #11410 to 2.3: Object initializers are called only once per object
  [Translator][FrameworkBundle] Added @ to the list of allowed chars in Translator
  [Process] Reduce I/O load on Windows platform
  [Form] Check if IntlDateFormatter constructor returned a valid object before using it