[Intl] Added "internal" tag to all classes under Symfony\Component\Intl\ResourceBundle

We didn't have this tag yet when this component was first written. The code in that
namespace is only used for resource bundle generation and was never meant for public
use.
minor #11891 [Intl] Added "internal" tag to all classes under Symfony\Component\Intl\ResourceBundle (webmozart)

This PR was merged into the 2.3 branch.

Discussion
----------

[Intl] Added "internal" tag to all classes under Symfony\Component\Intl\ResourceBundle

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

We didn't have this tag yet when this component was first written. The code in that
namespace is only used for resource bundle generation and was never meant for public
use.

We need to include in the update notes that users should check for usage of these classes.

Commits
-------

7fd5e8b [Intl] Added "internal" tag to all classes under Symfony\Component\Intl\ResourceBundle