[SPARK-48989][SQL][FOLLOWUP] Fix SubstringIndex codegen

### What changes were proposed in this pull request?
Fix genCode for `SubstringIndex`.

### Why are the changes needed?
GenCode was not fully correct in the original PR.

### Does this PR introduce _any_ user-facing change?
Yes, genCode now works properly for all collations.

### How was this patch tested?
Additional tests for other collations.

### Was this patch authored or co-authored using generative AI tooling?
No.

Closes apache#47610 from uros-db/followup-48989.

Authored-by: Uros Bojanic <157381213+uros-db@users.noreply.github.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

common/unsafe/src/main/java/org/apache/spark/sql/catalyst/util/CollationSupport.java

@@ -477,7 +477,7 @@ public static String genCode(final String string, final String delimiter,
       } else if (collation.supportsLowercaseEquality) {
         return String.format(expr + "Lowercase(%s, %s, %s)", string, delimiter, count);
       } else {
-        return String.format(expr + "ICU(%s, %s, %d, %s)", string, delimiter, count, collationId);
+        return String.format(expr + "ICU(%s, %s, %s, %d)", string, delimiter, count, collationId);
       }
     }
     public static UTF8String execBinary(final UTF8String string, final UTF8String delimiter,
@@ -490,8 +490,7 @@ public static UTF8String execLowercase(final UTF8String string, final UTF8String
     }
     public static UTF8String execICU(final UTF8String string, final UTF8String delimiter,
         final int count, final int collationId) {
-      return CollationAwareUTF8String.subStringIndex(string, delimiter, count,
-        collationId);
+      return CollationAwareUTF8String.subStringIndex(string, delimiter, count, collationId);
     }
   }
 

sql/core/src/test/scala/org/apache/spark/sql/StringFunctionsSuite.scala

@@ -425,12 +425,17 @@ class StringFunctionsSuite extends QueryTest with SharedSparkSession {
       Row("www.apache")
     )
 
+    // TODO SPARK-48779 Move E2E SQL tests with column input to collations.sql golden file.
     val testTable = "test_substring_index"
     withTable(testTable) {
       sql(s"CREATE TABLE $testTable (num int) USING parquet")
       sql(s"INSERT INTO $testTable VALUES (1), (2), (3), (NULL)")
-      val query = s"SELECT num, SUBSTRING_INDEX('a_a_a', '_', num) as sub_str FROM $testTable"
-      checkAnswer(sql(query), Seq(Row(1, "a"), Row(2, "a_a"), Row(3, "a_a_a"), Row(null, null)))
+      Seq("UTF8_BINARY", "UTF8_LCASE", "UNICODE", "UNICODE_CI").foreach(collation =>
+        withSQLConf(SQLConf.DEFAULT_COLLATION.key -> collation) {
+          val query = s"SELECT num, SUBSTRING_INDEX('a_a_a', '_', num) as sub_str FROM $testTable"
+          checkAnswer(sql(query), Seq(Row(1, "a"), Row(2, "a_a"), Row(3, "a_a_a"), Row(null, null)))
+        }
+      )
     }
   }