[SPARK-49992][SQL] Session level collation should not impact DDL queries

[stefankandic]

What changes were proposed in this pull request?

This PR proposes not using session-level collation in DDL commands, specifically in CREATE TABLE v2 and ALTER TABLE ADD/REPLACE COLUMNS commands.

Why are the changes needed?

The default collation for DDL commands should be tied to the object being created or altered (e.g., table, view, schema) rather than the session-level setting. Since object-level collations are not yet supported, we will assume the UTF8_BINARY collation by default for now.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Added new unit tests.

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

No.