[Form] Changed component to use the Intl component
[Form] Fixed failing tests
[Form] Adapted to latest Intl changes
[Form] Improved tests to use the IntlTestHelper class
merged branch bschussek/intl (PR #7386)

This PR was merged into the master branch.

Discussion
----------

[Intl] Refactored Locale component into two new components Icu and Intl

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | yes
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #5279
| License       | MIT
| Doc PR        | symfony/symfony-docs#2312

The Intl component is now a simple drop-in replacement layer for the C intl extension. Install it via Composer and have it available automatically if the intl extension is not available.

Additionally, the component ships data from the ICU library which can be accessed through the methods:

```php
use Symfony\Component\Intl\Intl;

Intl::getCurrencyBundle()->...
Intl::getLanguageBundle()->...
Intl::getLocaleBundle()->...
Intl::getRegionBundle()->...
```

If the intl extension is installed, Composer will install the ICU data for the ICU version in the intl extension. If the intl extension is not installed, Composer will use stub ICU data for the latest ICU version (see `Intl::getStubIcuVersion()`).

See the [README](/bschussek/symfony/blob/intl/src/Symfony/Component/Intl/README.md) for more information.

Todo:

- [x] finish the Intl README file
- [x] update the Icu README file
- [x] update the documentation
- [x] make parameter `$locale` optional (default to `\Locale::getDefault()`) in resource bundle methods
- [x] remove `(Icu)?Version::compare` calls in the tests
- [x] solve deployment problem when trying to install incompatible symfony/icu version listed in composer.lock

Create the following branches in the [Icu component](https://github.com/symfony/Icu):

- [x] 1.0.x
- [x] 1.1.x
- [x] 1.2.x

Commits
-------

9118b4a [Locale] Removed "Stub" prefixes in Intl component
b4cccfd [Intl] Removed "Stub" prefix from stub classes
60f31d1 [Intl] Improved inline documentation
c2d37e6 [Intl] Improved error messages in the build scripts
1249f01 [Intl] Added scripts to test the compatibility of various versions of symfony/icu with the ICU version installed on the system
9dbafd7 [Intl] Split update-stubs.php script into two scripts to function with the changed Icu component versioning
e2c11cb [Intl] Added a check for the ICU data version to IntlTestHelper to prevent the stub class tests from failing
427d24a [Intl] Outsourced bundle reader creation to Icu component
0160fd5 [Intl] Moved stub data to Icu component 1.0.x
dbca3b7 [Intl] Added empty directory needed for the tests
a717ce9 [Intl] Removed ICU version comparisons from the tests
5d17de5 [Intl] Fixed version comparisons in the transformation rules
470927d [Intl] Improved build scripts
aceb20d [Form] Improved tests to use the IntlTestHelper class
3dd75ff [Locale] Improved tests to use the IntlTestHelper class
03b78b0 [Validator] Improved tests to use the IntlTestHelper class
9d9c389 [Intl] Simplified tests
c55c4a2 [Intl] Only the StubNumberFormatterTest requires stub data
17a480b [Intl] Added IntlTestHelper class for convenience
1dcdcd3 [Locale] Fixed failing tests
f6b75b9 [Intl] Changed composer.json to disallow future versions of the Icu component
080c880 [Intl] Bumped the stub version to 50.1.2
dd2d013 [Intl] Improved the bundle compilation process
f47e60a [Intl] Fixed small bugs in the resource bundle transformation
467cc93 [Intl] Fixed various problems in the resource compilation process
4a5c453 [Intl] Moved the content of the README file to symfony/symfony-docs
9899de7 [Intl] Updated the README
bfec58a [Intl] Fixed flawed PHPDoc
21323ba [Intl] Updated the README file
209a9cb [Validator] Adapted to latest Intl changes
f2a0aec [Form] Adapted to latest Intl changes
0f6277f [Locale] Adapted to latest Intl changes
2cd1be8 [Intl] Made the $locale parameter optional in the bundle interfaces
b9e9cb2 [Intl] Added autoload.php which was ignored by .gitignore
838798f [Intl] Removed method IntlTestCase::skipIfInsufficientIcuVersion()
dde1d34 [Intl] Changed Intl::getIcuVersion() to return the stub version if the intl extension is not loaded
99f6f8a [Form] Fixed failing tests
5d0b849 Fixed PHPDoc
b60866c [Intl] Changed Intl::getStubIcuVersion() to Intl::getIcuStubVersion()
b902b6b [Locale] Added default locale
01d0ee8 [Validator] Changed component to use the Intl component
0c1fe39 [Form] Changed component to use the Intl component
5917a2e [Intl] Refactored Locale component into two new components Icu and Intl