[6020 ] Spark sql avg agg function support decimal

fix decimal avg function precision issue

Alchemy-item: [[6020 ] Spark sql avg agg function support decimal](#30 (comment)) commit 1/1 - a464bf5

Author: liujiayi771

velox/functions/lib/aggregates/AverageAggregateBase.cpp

@@ -21,7 +21,8 @@ namespace facebook::velox::functions::aggregate {
 void checkAvgIntermediateType(const TypePtr& type) {
   VELOX_USER_CHECK(
       type->isRow() || type->isVarbinary(),
-      "Input type for final average must be row type or varbinary type.");
+      "Input type for final average must be row type or varbinary type, find {}",
+      type->toString());
   if (type->kind() == TypeKind::VARBINARY) {
     return;
   }

velox/functions/lib/aggregates/DecimalAggregate.h

@@ -78,7 +78,7 @@ class DecimalAggregate : public exec::Aggregate {
   }
 
   int32_t accumulatorAlignmentSize() const override {
-    return static_cast<int32_t>(sizeof(int128_t));
+    return alignof(LongDecimalWithOverflowState);
   }
 
   void addRawInput(
@@ -275,7 +275,9 @@ class DecimalAggregate : public exec::Aggregate {
   }
 
   virtual TResultType computeFinalValue(
-      LongDecimalWithOverflowState* accumulator) = 0;
+      LongDecimalWithOverflowState* accumulator) {
+    return 0;
+  };
 
   void extractValues(char** groups, int32_t numGroups, VectorPtr* result)
       override {
@@ -327,11 +329,11 @@ class DecimalAggregate : public exec::Aggregate {
     }
   }
 
- private:
   inline LongDecimalWithOverflowState* decimalAccumulator(char* group) {
     return exec::Aggregate::value<LongDecimalWithOverflowState>(group);
   }
 
+ private:
   DecodedVector decodedRaw_;
   DecodedVector decodedPartial_;
 };