[fix](nereids)EliminateGroupBy rule should keep output's datatype unc…

…hanged (#45359)

Related PR: #28615

Problem Summary:
`select id, count(age) from t group by id`
consider t is unique table and it's unique key is id. The sql will be
convert to:
`select id, if(age is null, 0, 1) from t;`
count(age) is replaced by if(age is null, 0, 1). And we should keep
if(age is null, 0, 1)'s datatype same as count(age) which is bigint.

fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/EliminateGroupBy.java

@@ -30,7 +30,7 @@
 import org.apache.doris.nereids.trees.expressions.functions.agg.Min;
 import org.apache.doris.nereids.trees.expressions.functions.agg.Sum;
 import org.apache.doris.nereids.trees.expressions.functions.scalar.If;
-import org.apache.doris.nereids.trees.expressions.literal.Literal;
+import org.apache.doris.nereids.trees.expressions.literal.BigIntLiteral;
 import org.apache.doris.nereids.trees.plans.Plan;
 import org.apache.doris.nereids.util.ExpressionUtils;
 import org.apache.doris.nereids.util.PlanUtils;
@@ -84,12 +84,8 @@ public Rule build() {
                                         .castIfNotSameType(f.child(0), f.getDataType()), ne.getName()));
                             } else if (f instanceof Count) {
                                 newOutput.add((NamedExpression) ne.withChildren(
-                                        new If(
-                                            new IsNull(f.child(0)),
-                                            Literal.of(0),
-                                            Literal.of(1)
-                                        )
-                                ));
+                                        new If(new IsNull(f.child(0)), new BigIntLiteral(0),
+                                                new BigIntLiteral(1))));
                             } else {
                                 throw new IllegalStateException("Unexpected aggregate function: " + f);
                             }

fe/fe-core/src/test/java/org/apache/doris/nereids/rules/rewrite/EliminateGroupByTest.java

@@ -94,6 +94,7 @@ void eliminateCount() {
                         logicalEmptyRelation().when(p -> p.getProjects().get(0).toSql().equals("id")
                                 && p.getProjects().get(1).toSql()
                                 .equals("if(age IS NULL, 0, 1) AS `if(age IS NULL, 0, 1)`")
+                                && p.getProjects().get(1).getDataType().isBigIntType()
                         )
                 );
     }