Remove placeholder param data feature from core features

[wilkerlucio]

The feature of always using placeholder parameters as a description to override the entity data needs to be revised. The issue is that forcing that behavior makes it difficult to implement custom behavior for params on placeholders.

So to keep Pathom flexible for the user to make its own semantics, I will remove this feature.

For users that want to retain the behavior, I'll provide a plugin that re-implements the same behavior.

[wilkerlucio]

Now there is a new plugin pbip/placeholder-data-params which gets back the same behavior for users that want to keep it.