Actor handler in r2dbc and dynamodb projection

[patriknw]

In the restructuring in #1386 the actor init was never fixed. We need to find a solution for that. Right now, I think, actor handler isn't working with r2dbc projection.

https://github.com/akka/akka-projection/pull/1386/files#r2568444676

[patriknw]

I started implementing this, and it became yet another workaround the structure from the original structure. It turns out that this has never worked for r2dbc, and it wasn't introduced in #1386

The problem is that the actorHandlerInit in FunctionHandlerStrategy tries to see if the created handler is a ActorHandlerInit, but for r2dbc we have the adapters in between.

Since it seems nobody has complained I don't think we should add it. We should instead consider a redesign of the internals.