Add some const decorations

These mainly help understanding the function signatures better.

src/backend/executor/execExpr.c

@@ -3314,8 +3314,8 @@ ExprState *
 ExecBuildGroupingEqual(TupleDesc ldesc, TupleDesc rdesc,
 					   const TupleTableSlotOps *lops, const TupleTableSlotOps *rops,
 					   int numCols,
-					   AttrNumber *keyColIdx,
-					   Oid *eqfunctions,
+					   const AttrNumber *keyColIdx,
+					   const Oid *eqfunctions,
 					   PlanState *parent)
 {
 	ExprState  *state = makeNode(ExprState);

src/backend/executor/execGrouping.c

@@ -59,8 +59,8 @@ static int	TupleHashTableMatch(struct tuplehash_hash *tb, const MinimalTuple tup
 ExprState *
 execTuplesMatchPrepare(TupleDesc desc,
 					   int numCols,
-					   AttrNumber *keyColIdx,
-					   Oid *eqOperators,
+					   const AttrNumber *keyColIdx,
+					   const Oid *eqOperators,
 					   PlanState *parent)
 {
 	Oid		   *eqFunctions = (Oid *) palloc(numCols * sizeof(Oid));
@@ -94,7 +94,7 @@ execTuplesMatchPrepare(TupleDesc desc,
  */
 void
 execTuplesHashPrepare(int numCols,
-					  Oid *eqOperators,
+					  const Oid *eqOperators,
 					  Oid **eqFuncOids,
 					  FmgrInfo **hashFunctions)
 {
@@ -153,7 +153,7 @@ TupleHashTable
 BuildTupleHashTable(PlanState *parent,
 					TupleDesc inputDesc,
 					int numCols, AttrNumber *keyColIdx,
-					Oid *eqfuncoids,
+					const Oid *eqfuncoids,
 					FmgrInfo *hashfunctions,
 					long nbuckets, Size additionalsize,
 					MemoryContext tablecxt, MemoryContext tempcxt,

src/include/executor/executor.h

@@ -108,17 +108,17 @@ extern bool execCurrentOf(CurrentOfExpr *cexpr,
  */
 extern ExprState *execTuplesMatchPrepare(TupleDesc desc,
 					   int numCols,
-					   AttrNumber *keyColIdx,
-					   Oid *eqOperators,
+					   const AttrNumber *keyColIdx,
+					   const Oid *eqOperators,
 					   PlanState *parent);
 extern void execTuplesHashPrepare(int numCols,
-					  Oid *eqOperators,
+					  const Oid *eqOperators,
 					  Oid **eqFuncOids,
 					  FmgrInfo **hashFunctions);
 extern TupleHashTable BuildTupleHashTable(PlanState *parent,
 					TupleDesc inputDesc,
 					int numCols, AttrNumber *keyColIdx,
-					Oid *eqfuncoids,
+					const Oid *eqfuncoids,
 					FmgrInfo *hashfunctions,
 					long nbuckets, Size additionalsize,
 					MemoryContext tablecxt,
@@ -244,8 +244,8 @@ extern ExprState *ExecBuildAggTrans(AggState *aggstate, struct AggStatePerPhaseD
 extern ExprState *ExecBuildGroupingEqual(TupleDesc ldesc, TupleDesc rdesc,
 					   const TupleTableSlotOps *lops, const TupleTableSlotOps *rops,
 					   int numCols,
-					   AttrNumber *keyColIdx,
-					   Oid *eqfunctions,
+					   const AttrNumber *keyColIdx,
+					   const Oid *eqfunctions,
 					   PlanState *parent);
 extern ProjectionInfo *ExecBuildProjectionInfo(List *targetList,
 						ExprContext *econtext,