[SPARK-54584][SS] Adding `.name()` to DataStreamReader to enable naming streaming sources

[ericm-db]

What changes were proposed in this pull request?

We want to add .name() to the DataStreamReader to enable naming streaming sources, which will allow users to add, remove and reorder sources. This API is currently package-private and not user-accessible.

Why are the changes needed?

Currently, if a user tries to make any change to their streaming source in their query, the query will fail as the way we compare sources (via ordinal in the logical plan) are incompatible. Keying by name as opposed to ordinal is far less brittle

Does this PR introduce any user-facing change?

No

How was this patch tested?

Unit tests

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

No