[SPARK-51732][SQL] Apply rpad on attributes with same ExprId if they need to be deduplicated

[mihailotim-db]

What changes were proposed in this pull request?

This PR fixes a case where rpad is not applied on attributes that have the same ExprId even though those attributes should be deduplicated.

Why are the changes needed?

For example, consider the following query:

CREATE OR REPLACE TABLE t(a CHAR(50)); 
SELECT t1.aFROM t t1 
WHERE (SELECT count(*) AS item_cnt FROM t t2 WHERE (t1.a = t2.a)) > 0

In the above case, ApplyCharTypePadding will run for subquery where t1.a and t2.a will reference the same ExprId, therefore we won't apply rpad. However, after DeduplicateRelations runs for outer query, t1.a and t2.a will get different ExprIds and would therefore need rpad. However, this doesn't happen because ApplyCharTypePadding for outer query does not recurse into the subquery.

On the other hand, for a query:

SELECT t1.a
FROM t t1, t t2
WHERE t1.a = t2.a 

ApplyCharTypePadding will correctly add rpad to both t1.a and t2.a because attributes will first be deduplicated.

In particular, this fixes a code-path when readSideCharPadding is off and LEGACY_NO_CHAR_PADDING_IN_PREDICATE is also false

Does this PR introduce any user-facing change?

How was this patch tested?

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

No