Improve performance of PagesIndexComparator for strings

Made changes to prefer adapting ordering operator from the
more efficient version of DefaultOrderingOperators#comparisonOperator
that avoids unnecessary copies of Slice for comparison

BenchmarkPagesIndexOrdering.benchmarkQuickSort
(numberOfChannels)  (typeName)  Mode  Cnt  Before score    After score    Unit
                 1      BIGINT  avgt  20   29.536 ± 0.696  28.299 ± 0.344 ms/op
                 1     VARCHAR  avgt  20   66.897 ± 1.914  53.538 ± 0.635 ms/op
                10      BIGINT  avgt  20   36.965 ± 0.270  36.577 ± 0.605 ms/op
                10     VARCHAR  avgt  20   79.887 ± 3.077  60.413 ± 0.678 ms/op

Author: raunaqmorarka

core/trino-spi/src/main/java/io/trino/spi/type/TypeOperators.java

@@ -43,6 +43,7 @@
 import static io.trino.spi.function.InvocationConvention.InvocationArgumentConvention.FLAT;
 import static io.trino.spi.function.InvocationConvention.InvocationArgumentConvention.NEVER_NULL;
 import static io.trino.spi.function.InvocationConvention.InvocationArgumentConvention.NULL_FLAG;
+import static io.trino.spi.function.InvocationConvention.InvocationArgumentConvention.VALUE_BLOCK_POSITION_NOT_NULL;
 import static io.trino.spi.function.InvocationConvention.InvocationReturnConvention.BLOCK_BUILDER;
 import static io.trino.spi.function.InvocationConvention.InvocationReturnConvention.FAIL_ON_NULL;
 import static io.trino.spi.function.InvocationConvention.simpleConvention;
@@ -496,7 +497,12 @@ private OperatorMethodHandle generateOrderingOperator(OperatorConvention operato
             SortOrder sortOrder = operatorConvention.sortOrder().orElseThrow(() -> new IllegalArgumentException("Operator convention does not contain a sort order"));
             OperatorType comparisonType = operatorConvention.operatorType();
             if (operatorConvention.callingConvention().getArgumentConventions().equals(List.of(BLOCK_POSITION, BLOCK_POSITION))) {
-                OperatorConvention comparisonOperator = new OperatorConvention(operatorConvention.type(), comparisonType, Optional.empty(), simpleConvention(FAIL_ON_NULL, BLOCK_POSITION, BLOCK_POSITION));
+                OperatorConvention comparisonOperator = new OperatorConvention(
+                        operatorConvention.type(),
+                        comparisonType,
+                        Optional.empty(),
+                        // null positions are handled separately in adaptBlockPositionComparisonToOrdering and not used in the comparison
+                        simpleConvention(FAIL_ON_NULL, BLOCK_POSITION_NOT_NULL, BLOCK_POSITION_NOT_NULL));
                 MethodHandle comparisonInvoker = adaptOperator(comparisonOperator);
                 return adaptBlockPositionComparisonToOrdering(sortOrder, comparisonInvoker);
             }
@@ -538,7 +544,7 @@ private static int getScore(OperatorMethodHandle operatorMethodHandle)
             if (argument == NULL_FLAG || argument == FLAT) {
                 score += 100;
             }
-            else if (argument == BLOCK_POSITION) {
+            else if (argument == BLOCK_POSITION || argument == VALUE_BLOCK_POSITION_NOT_NULL) {
                 score += 1;
             }
         }