…ing cache. (jakzal)

This PR was merged into the 2.5 branch.

Discussion
----------

[FrameworkBundle] Allow custom services for validator mapping cache.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #12803
| License       | MIT
| Doc PR        | -

#9892 introduced `DoctrineCache`, but it's not really used by the FrameworkBundle. This was overlooked, therefore I think it should go into 2.5.

This PR will let us to configure a service id, instead of a driver name. The only exception is apc, which is converted to `validator.mapping.cache.apc` to keep BC.

Examples:

```yaml
framework:
    validation:
        cache: apc # converted to validator.mapping.cache.apc
```

```yaml
framework:
    validation:
        cache: my_custom_cache_service
```

It would be nice to be able to provide a doctrine service id, instead of `CacheInterface` implementation. It could be automatically decorated with `DoctrineCache`:

```yaml
framework:
    validation:
        cache:
            doctrine: my_doctrine_cache_service # could be provided by DoctrineCacheBundle
```

I'll work on it next.

Commits
-------

4cdcf10 [FrameworkBundle] Allow custom services for validator mapping cache.