[refactor](Nereids) remove trick datatype code in Expression (#16365)

Since we already do typeCoercion bottom-up in binding step.
The trick codes of dataType in Expression are useless.
This PR try to remove them.

Author: morrySnow

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/expressions/Add.java

@@ -44,7 +44,7 @@ public Expression withChildren(List<Expression> children) {
 
     @Override
     public DataType getDataType() {
-        return left().getDataType().promotion();
+        return super.getDataType().promotion();
     }
 
     @Override

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/expressions/BinaryArithmetic.java

@@ -23,7 +23,6 @@
 import org.apache.doris.nereids.trees.expressions.typecoercion.ImplicitCastInputTypes;
 import org.apache.doris.nereids.trees.expressions.visitor.ExpressionVisitor;
 import org.apache.doris.nereids.types.DataType;
-import org.apache.doris.nereids.util.TypeCoercionUtils;
 
 /**
  * binary arithmetic operator. Such as +, -, *, /.
@@ -43,17 +42,7 @@ public Operator getLegacyOperator() {
 
     @Override
     public DataType getDataType() throws UnboundException {
-        if (left().getDataType().equals(right().getDataType())) {
-            return left().getDataType();
-        } else {
-            try {
-                return TypeCoercionUtils.findCommonNumericsType(left().getDataType(), right().getDataType());
-            } catch (Exception e) {
-                return TypeCoercionUtils.findTightestCommonType(this,
-                                left().getDataType(), right().getDataType())
-                        .orElseGet(() -> left().getDataType());
-            }
-        }
+        return left().getDataType();
     }
 
     @Override

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/expressions/CaseWhen.java

@@ -21,7 +21,6 @@
 import org.apache.doris.nereids.trees.expressions.functions.ExpressionTrait;
 import org.apache.doris.nereids.trees.expressions.visitor.ExpressionVisitor;
 import org.apache.doris.nereids.types.DataType;
-import org.apache.doris.nereids.util.TypeCoercionUtils;
 
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
@@ -78,13 +77,7 @@ public <R, C> R accept(ExpressionVisitor<R, C> visitor, C context) {
 
     @Override
     public DataType getDataType() {
-        DataType outputType = child(0).getDataType();
-        for (Expression child : children) {
-            DataType tempType = outputType;
-            outputType = TypeCoercionUtils.findTightestCommonType(null,
-                    outputType, child.getDataType()).orElse(tempType);
-        }
-        return outputType;
+        return child(0).getDataType();
     }
 
     @Override

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/expressions/Multiply.java

@@ -22,7 +22,6 @@
 import org.apache.doris.nereids.types.DataType;
 import org.apache.doris.nereids.types.coercion.AbstractDataType;
 import org.apache.doris.nereids.types.coercion.NumericType;
-import org.apache.doris.nereids.util.TypeCoercionUtils;
 
 import com.google.common.base.Preconditions;
 
@@ -45,12 +44,7 @@ public Expression withChildren(List<Expression> children) {
 
     @Override
     public DataType getDataType() {
-        DataType rightType = child(0).getDataType();
-        DataType leftType = child(1).getDataType();
-        DataType outputType = TypeCoercionUtils.findTightestCommonType(this,
-                rightType, leftType).orElseGet(() -> rightType);
-        outputType = outputType.promotion();
-        return outputType;
+        return super.getDataType().promotion();
     }
 
     @Override

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/expressions/Subtract.java

@@ -44,7 +44,7 @@ public Expression withChildren(List<Expression> children) {
 
     @Override
     public DataType getDataType() {
-        return left().getDataType().promotion();
+        return super.getDataType().promotion();
     }
 
     @Override