[SPARK-46961][SS] Using ProcessorContext to store and retrieve handle

[ericm-db]

What changes were proposed in this pull request?

Setting the processorHandle as a part of the statefulProcessor, so that the user doesn't have to explicitly keep track of it, and can instead simply call getStatefulProcessorHandle

Why are the changes needed?

This enhances the usability of the State API

Does this PR introduce any user-facing change?

Yes, this is an API change. This enhances usability of the StatefulProcessorHandle and the TransformWithState operator.

How was this patch tested?

Existing unit tests are sufficient

Was this patch authored or co-authored using generative AI tooling?

No