Add Postgres compliant name aliasing for String Functions. (#12795)

Certain String function names are not Postgres compliant, added aliasing
to fix that.
- left
- right
- split_part
- string_to_array

pinot-common/src/main/java/org/apache/pinot/common/function/TransformFunctionType.java

@@ -180,7 +180,7 @@ public enum TransformFunctionType {
   // string functions
   SPLIT("split", ReturnTypes.TO_ARRAY, OperandTypes.family(
       ImmutableList.of(SqlTypeFamily.CHARACTER, SqlTypeFamily.CHARACTER, SqlTypeFamily.INTEGER),
-      ordinal -> ordinal > 1), "split"),
+      ordinal -> ordinal > 1), "split", "string_to_array"),
 
   // array functions
   // The only column accepted by "cardinality" function is multi-value array, thus putting "cardinality" as alias.

pinot-common/src/main/java/org/apache/pinot/common/function/scalar/StringFunctions.java

@@ -243,7 +243,7 @@ public static String rtrim(String input) {
    * @param input
    * @return get substring starting from the first index and extending upto specified length.
    */
-  @ScalarFunction
+  @ScalarFunction(names = {"leftSubStr", "left"})
   public static String leftSubStr(String input, int length) {
     return StringUtils.left(input, length);
   }
@@ -253,7 +253,7 @@ public static String leftSubStr(String input, int length) {
    * @param input
    * @return get substring ending at the last index with specified length
    */
-  @ScalarFunction
+  @ScalarFunction(names = {"rightSubStr", "right"})
   public static String rightSubStr(String input, int length) {
     return StringUtils.right(input, length);
   }
@@ -565,7 +565,7 @@ public static String normalize(String input, String form) {
    * @param delimiter
    * @return splits string on specified delimiter and returns an array.
    */
-  @ScalarFunction
+  @ScalarFunction(names = {"split", "string_to_array"})
   public static String[] split(String input, String delimiter) {
     return StringUtils.splitByWholeSeparator(input, delimiter);
   }
@@ -576,7 +576,7 @@ public static String[] split(String input, String delimiter) {
    * @param limit
    * @return splits string on specified delimiter limiting the number of results till the specified limit
    */
-  @ScalarFunction
+  @ScalarFunction(names = {"split", "string_to_array"})
   public static String[] split(String input, String delimiter, int limit) {
     return StringUtils.splitByWholeSeparator(input, delimiter, limit);
   }
@@ -588,7 +588,7 @@ public static String[] split(String input, String delimiter, int limit) {
    * @param index
    * @return splits string on specified delimiter and returns String at specified index from the split.
    */
-  @ScalarFunction
+  @ScalarFunction(names = {"splitPart", "split_part"})
   public static String splitPart(String input, String delimiter, int index) {
     String[] splitString = StringUtils.splitByWholeSeparator(input, delimiter);
     if (index < splitString.length) {