[SPARK-56611][SQL] Fix ALTER TABLE RENAME TO with catalog-qualified and table-only targets

[lunar-shadow]

What changes were proposed in this pull request?

This fixes ALTER TABLE ... RENAME TO in V2 catalogs for two cases that weren't handled correctly:

• When the target name is catalog-qualified
• When the target is just a table name (no namespace)

Changes:

• Strip the catalog prefix from the target when it matches the source catalog
• Inherit source namespace when target is table-only
• Add tests covering the above cases

Why are the changes needed?

Right now, rename behaves incorrectly in a few scenarios.

For example:

ALTER TABLE testcat.ns.t1 RENAME TO testcat.ns.t2;

fails because asIdentifier treats everything except the last part as the namespace. That means the catalog name (testcat) incorrectly ends up inside the namespace:

Identifier.of(["testcat", "ns"], "t2")

instead of:

Identifier.of(["ns"], "t2")

Similarly:

ALTER TABLE testcat.ns.t1 RENAME TO t2;

creates an identifier with an empty namespace, instead of inheriting ns from the source table.

Steps to reproduce:

CREATE TABLE testcat.ns.t1 USING foo AS SELECT 1 AS id;
ALTER TABLE testcat.ns.t1 RENAME TO testcat.ns.t2;

This fails with a namespace resolution error due to the catalog being treated as part of the namespace.

Does this PR introduce any user-facing change?

Yes.

• Catalog-qualified renames like ALTER TABLE catalog.ns.t1 RENAME TO catalog.ns.t2 now work correctly
• Renaming to a table-only name (e.g., RENAME TO t2) now correctly keeps the original namespace
• Cross-namespace renames (e.g., RENAME TO other_ns.t2) continue to work as before

How was this patch tested?

Added tests in DataSourceV2SQLSuite covering catalog-qualified renames, table-only renames, and cross-namespace renames.

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

No