[SPARK-50245][SQL][TESTS] Extended CollationSuite and added tests whe…

…re SortMergeJoin is forced

### What changes were proposed in this pull request?

I propose extending existing tests in `CollationSuite` and add cases where `SortMergeJoin` is forced and tested for correctness and use of `CollationKey`.

### Why are the changes needed?

These changes are needed to properly test behavior of join with collated data when different configs are enabled.

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

The change is a test itself.

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

No.

Closes #48774 from vladanvasi-db/vladanvasi-db/collation-suite-test-extension.

Authored-by: Vladan Vasić <[email protected]>
Signed-off-by: Max Gekk <[email protected]>