Added toStringList function

- This function is inspired by the "tostringlist" function in OpenCypher.https://neo4j.com/docs/cypher-manual/current/functions/list/#functions-tostringlist
- toStringList() converts a list of values and returns a list of string values. If any values are not convertible to string they will be null in the list returned.
- A list containing the converted elements; depending on the input value a converted value is either a string value or null.
- Also added the regression tests
- This PR fix the issue apache#1073

Author: M4rcxs

src/backend/utils/adt/agtype.c

@@ -6159,8 +6159,6 @@ Datum age_tostringlist(PG_FUNCTION_ARGS)
     agtype_value string_elem;
     int count;
     int i;
-    float float_num;
-    int float_size;
     char buffer[64];
 
     /* check for null */
@@ -6214,7 +6212,6 @@ Datum age_tostringlist(PG_FUNCTION_ARGS)
 
         case AGTV_FLOAT:
 
-            float_num = elem->val.float_value;
             sprintf(buffer, "%.*g", DBL_DIG, elem->val.float_value);
             string_elem.val.string.val = pstrdup(buffer);
             string_elem.val.string.len = strlen(buffer);
@@ -6225,7 +6222,7 @@ Datum age_tostringlist(PG_FUNCTION_ARGS)
 
         case AGTV_INTEGER:
 
-            sprintf(buffer, "%d", elem->val.int_value);
+            sprintf(buffer, "%ld", elem->val.int_value);
             string_elem.val.string.val = pstrdup(buffer);
             string_elem.val.string.len = strlen(buffer);