[Enhancement](length) Support alias OCTET_LENGTH for function LENGTH (#57369)

An alias for `LENGTH`(see [OCTET_LENGTH in
MySQL](https://dev.mysql.com/doc/refman/8.4/en/string-functions.html#function_octet-length):
[OCTET_LENGTH()](https://dev.mysql.com/doc/refman/8.4/en/string-functions.html#function_octet-length)
is a synonym for
[LENGTH()](https://dev.mysql.com/doc/refman/8.4/en/string-functions.html#function_length).)

```text
mysql> SELECT OCTET_LENGTH('abc');
+---------------------+
| OCTET_LENGTH('abc') |
+---------------------+
|                   3 |
+---------------------+

mysql> SELECT OCTET_LENGTH('你好');
+------------------------+
| OCTET_LENGTH('你好')   |
+------------------------+
|                      6 |
+------------------------+
```

Author: linrrzqqq

be/src/vec/functions/function_string.cpp

@@ -1457,6 +1457,7 @@ void register_function_string(SimpleFunctionFactory& factory) {
     factory.register_alias(FunctionStringDigestMulti<SM3Sum>::name, "sm3");
     factory.register_alias(FunctionStringDigestSHA1::name, "sha");
     factory.register_alias(FunctionStringLocatePos::name, "position");
+    factory.register_alias(FunctionStringLength::name, "octet_length");
 }
 
 } // namespace doris::vectorized

fe/fe-core/src/main/java/org/apache/doris/catalog/BuiltinScalarFunctions.java

@@ -832,7 +832,7 @@ public class BuiltinScalarFunctions implements FunctionHelper {
             scalar(Lcm.class, "lcm"),
             scalar(Least.class, "least"),
             scalar(Left.class, "left", "strleft"),
-            scalar(Length.class, "length"),
+            scalar(Length.class, "length", "octet_length"),
             scalar(Crc32.class, "crc32"),
             scalar(Crc32Internal.class, "crc32_internal"),
             scalar(Like.class, "like"),

regression-test/suites/nereids_function_p0/scalar_function/L.groovy

@@ -73,6 +73,18 @@ suite("nereids_scalar_fn_L") {
 	qt_sql_length_Varchar_notnull "select length(kvchrs1) from fn_test_not_nullable order by kvchrs1"
 	qt_sql_length_String "select length(kstr) from fn_test order by kstr"
 	qt_sql_length_String_notnull "select length(kstr) from fn_test_not_nullable order by kstr"
+	def length_str = sql """select length(kvchrs1) from fn_test order by kvchrs1"""
+	def octet_length_str = sql """select octet_length(kvchrs1) from fn_test order by kvchrs1"""
+	assertEquals(length_str, octet_length_str)
+	length_str = sql """select length(kvchrs1) from fn_test_not_nullable order by kvchrs1"""
+	octet_length_str = sql """select length(kvchrs1) from fn_test_not_nullable order by kvchrs1"""
+	assertEquals(length_str, octet_length_str)
+	length_str = sql """select length(kstr) from fn_test order by kstr"""
+	octet_length_str = sql """select octet_length(kstr) from fn_test order by kstr"""
+	assertEquals(length_str, octet_length_str)
+	length_str = sql """select length(kstr) from fn_test_not_nullable order by kstr"""
+	octet_length_str = sql """select octet_length(kstr) from fn_test_not_nullable order by kstr"""
+	assertEquals(length_str, octet_length_str)
 	qt_sql_like_Varchar_Varchar "select like(kvchrs1, kvchrs2) from fn_test order by kvchrs1"
 	qt_sql_like_Varchar_Varchar_not_null "select like(kvchrs1, kvchrs2) from fn_test_not_nullable order by kvchrs1"
 	qt_sql_ln_Double "select ln(kdbl) from fn_test order by kdbl"