[fix](fold) fixed an issue with be computing constants (#43410)

### What problem does this PR solve?

issue close: #43061

1、Problem
When enable_fold_constant_by_be=true is set,the results of
between below queries are inconsistent

select hex(from_base64('wr2JEDVXzL9+2XtRhgIloA==')) 
+----------------------------------------------+
| hex(from_base64('wr2JEDVXzL9+2XtRhgIloA==')) |
+----------------------------------------------+
| C2BD89103557CCBF7ED97B51860225A0             |
+----------------------------------------------+

select hex(s) from (select from_base64('wr2JEDVXzL9+2XtRhgIloA==') as s) t 
+--------------------------------------------------+
| hex(s)                                           |
+--------------------------------------------------+
| C2BDEFBFBD103557CCBF7EEFBFBD7B51EFBFBD0225EFBFBD |
+--------------------------------------------------+

2、mysql results

select hex(s) from (select from_base64('wr2JEDVXzL9+2XtRhgIloA==') as s) t;
+----------------------------------+
| hex(s)                           |
+----------------------------------+
| C2BD89103557CCBF7ED97B51860225A0 |
+----------------------------------+

3、cause
When processing binary data such as FromBase64, BE will return the
original binary data through the bytesValue field, and the previous code
only uses the stringValue field, resulting in the binary data being
corrupted during the string encoding conversion process

fe/fe-core/src/main/java/org/apache/doris/nereids/rules/expression/rules/FoldConstantRuleOnBE.java

@@ -487,8 +487,16 @@ public static List<Literal> getResultExpression(DataType type, PValues resultCon
         } else if (type.isStringLikeType()) {
             int num = resultContent.getStringValueCount();
             for (int i = 0; i < num; ++i) {
-                Literal literal = new StringLiteral(resultContent.getStringValue(i));
-                res.add(literal);
+                // get the raw byte data to avoid character encoding conversion problems
+                ByteString bytesValues = resultContent.getBytesValue(i);
+                // use UTF-8 encoding to ensure proper handling of binary data
+                String stringValue = bytesValues.toStringUtf8();
+                // handle special NULL value cases
+                if ("\\N".equalsIgnoreCase(stringValue) && resultContent.hasHasNull()) {
+                    res.add(new NullLiteral(type));
+                } else {
+                    res.add(new StringLiteral(stringValue));
+                }
             }
         } else if (type.isArrayType()) {
             ArrayType arrayType = (ArrayType) type;

fe/fe-core/src/test/java/org/apache/doris/nereids/trees/expressions/LiteralTest.java

@@ -233,7 +233,9 @@ public void testGetResultExpressionStruct() {
         PValues.Builder resultContentBuilder = PValues.newBuilder();
         for (int i = 0; i < elementsArray.length; i = i + 2) {
             childBuilder1.addInt32Value(elementsArray[i]);
-            childBuilder2.addStringValue("str" + (i + 1));
+            String strValue = "str" + (i + 1);
+            childBuilder2.addStringValue(strValue);
+            childBuilder2.addBytesValue(com.google.protobuf.ByteString.copyFromUtf8(strValue));
         }
         childBuilder1.setType(childTypeBuilder1.build());
         childBuilder2.setType(childTypeBuilder2.build());
@@ -280,7 +282,9 @@ public void testGetResultExpressionStructArray() {
         PValues.Builder resultContentBuilder = PValues.newBuilder();
         for (int i = 0; i < elementsArray.length; i = i + 2) {
             childBuilder1.addInt32Value(elementsArray[i]);
-            childBuilder2.addStringValue("str" + (i + 1));
+            String strValue = "str" + (i + 1);
+            childBuilder2.addStringValue(strValue);
+            childBuilder2.addBytesValue(com.google.protobuf.ByteString.copyFromUtf8(strValue));
         }
         childBuilder1.setType(childTypeBuilder1.build());
         childBuilder2.setType(childTypeBuilder2.build());

regression-test/data/nereids_p0/expression/fold_constant/fold_constant_by_be.out

@@ -1,4 +1,10 @@
 -- This file is automatically generated. You should know what you did if you want to edit this
+-- !sql --
+C2BD89103557CCBF7ED97B51860225A0
+
+-- !sql --
+C2BD89103557CCBF7ED97B51860225A0
+
 -- !sql_1 --
 80000
 

regression-test/suites/nereids_p0/expression/fold_constant/fold_constant_by_be.groovy

@@ -22,6 +22,9 @@ suite("fold_constant_by_be") {
     sql 'set enable_fallback_to_original_planner=false'
     sql 'set enable_fold_constant_by_be=true'
 
+    qt_sql """ select hex(from_base64('wr2JEDVXzL9+2XtRhgIloA==')); """
+    qt_sql """ select hex(s) from (select from_base64('wr2JEDVXzL9+2XtRhgIloA==') as s) t; """
+
     test {
         sql '''
             select if(
@@ -32,8 +35,8 @@ suite("fold_constant_by_be") {
         result([['9999-07-31']])
     }
 
-    sql """ 
-        CREATE TABLE IF NOT EXISTS str_tb (k1 VARCHAR(10) NULL, v1 STRING NULL) 
+    sql """
+        CREATE TABLE IF NOT EXISTS str_tb (k1 VARCHAR(10) NULL, v1 STRING NULL)
         UNIQUE KEY(k1) DISTRIBUTED BY HASH(k1) BUCKETS 5 properties("replication_num" = "1");
     """
 
@@ -53,7 +56,7 @@ suite("fold_constant_by_be") {
 
     sql 'set query_timeout=12;'
     qt_sql "select sleep(sign(1)*5);"
-    
+
     explain {
         sql("verbose select substring('123456', 1, 3)")
         contains "varchar(3)"
@@ -71,7 +74,7 @@ suite("fold_constant_by_be") {
                     col_varchar_1000__undef_signed varchar(1000)  null  ,
                     col_varchar_1000__undef_signed_not_null varchar(1000)  not null  ,
                     col_varchar_1001__undef_signed varchar(1001)  null  ,
-                    col_varchar_1001__undef_signed_not_null varchar(1001)  not null  
+                    col_varchar_1001__undef_signed_not_null varchar(1001)  not null
                     ) engine=olap
                     DUPLICATE KEY(pk, col_char_255__undef_signed, col_char_100__undef_signed)
                     distributed by hash(pk) buckets 10