Rethink: "Deprecate extension via schema manipulation events"

[lyrixx]

Hello,

I had to fix this deprecation, and honestly, I'm not really happy with the result.

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My use case is the following:

I have some special columns in my DB that my Entity does not need. It's a speciel fields for indexing data. See https://www.postgresql.org/docs/current/datatype-textsearch.html

So, in order to avoid a diff each time I run doctrine:scheme:validate or doctrine:migration:diff I added a small listener to remove the column, and the indices.

Today, I migrated to DBAL 4, and I had to replace this. I may be wrong, but I ended with this commit :

jolicode/qotd@dcd5313

1. There is no interface on AbstractSchemaManager. So I needed to "implements" some protected method, But there a not used at all
2. There is a lot of method to decorate
3. Schema::getSchemaConfig() does not exist

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I think this use case is a bit common, so I'm proposing the following

1. Create a SchemaManager Interface
2. If possible, an AbstractDecoratedSchemaManager (a bit like AbstractDriverMiddleware)
3. Add Schema::getSchemaConfig()

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WDYT?