Add symfony cache pool support

[alcaeus]

This PR adds support for using a symfony/cache pool directly without having to create extra services. It makes the default configuration from the recipe a lot shorter:

 doctrine:
     orm:
         auto_generate_proxy_classes: false
         metadata_cache_driver:
-            type: service
-            id: doctrine.system_cache_provider
+            type: pool
+            pool: doctrine.system_cache_pool
         query_cache_driver:
-            type: service
-            id: doctrine.system_cache_provider
+            type: pool
+            pool: doctrine.system_cache_pool
         result_cache_driver:
-            type: service
-            id: doctrine.result_cache_provider
+            type: pool
+            pool: doctrine.result_cache_pool
 
-services:
-    doctrine.result_cache_provider:
-        class: Symfony\Component\Cache\DoctrineProvider
-        public: false
-        arguments:
-            - '@doctrine.result_cache_pool'
-    doctrine.system_cache_provider:
-        class: Symfony\Component\Cache\DoctrineProvider
-        public: false
-        arguments:
-            - '@doctrine.system_cache_pool'
-
 framework:
     cache:
         pools:
             doctrine.result_cache_pool:
                 adapter: cache.app
             doctrine.system_cache_pool:
                 adapter: cache.system

The added normalisation step in Configuration is to add a type field to the cache configuration when using the cache_provider setting for DoctrineCacheBundle. This makes the entire block of creating the correct cache alias simpler.

With this PR, using the new pool setting is optional, as is the dependency on symfony/cache. In a future PR, we'll be deprecating support for declaring caches through DoctrineCacheBundle, leaving only the id and pool cache types. Support for DoctrineCacheBundle will be dropped in DoctrineBundle 2.0.

This PR was created during the Symfony Hackathon sponsored by the EU-FOSSA 2 program.

[nicolas-grekas]

LGTM, thanks!

[Koc]

@alcaeus will you update default recipe for that change?

[alcaeus]

That change will come in the next few days 👍