MDEV-22224: Support JSON Path negative index

This patch can be viewed as combination of two parts:
1) Enabling '-' in the path so that the parser does not give out a warning.
2) Setting the negative index to a correct value and returning the
   appropriate value.

1) To enable using the negative index in the path:
To make the parser not return warning when negative index is used in path
'-' needs to be allowed in json path characters. P_NEG is added
to enable this and is made recognizable by setting the 45th index of
json_path_chr_map[] to P_NEG (instead of previous P_ETC)
because 45 corresponds to '-' in unicode.
When the path is being parsed and '-' is encountered, the parser should
recognize it as parsing '-' sign, so a new json state PS_NEG is required.
When the state is PS_NEG, it means that a negative integer is
going to be parsed so set is_negative_index of current step to 1 and
n_item is set accordingly when integer is encountered after '-'.
Next proceed with parsing rest of the path and get the correct path.
Next thing is parsing the json and returning correct value.

2) Setting the negative index to a correct value and returning the value:
While parsing json if we encounter array and the path step for the array
is a negative index (n_item < 0), then we can count the number of elements
in the array and set n_item to correct corresponding value. This is done in
json_skip_array_and_count.

include/json_lib.h

@@ -83,7 +83,8 @@ enum json_path_step_types
   JSON_PATH_KEY_WILD= 1+4,
   JSON_PATH_KEY_DOUBLEWILD= 1+8,
   JSON_PATH_ARRAY_WILD= 2+4,
-  JSON_PATH_ARRAY_DOUBLEWILD= 2+8
+  JSON_PATH_ARRAY_DOUBLEWILD= 2+8,
+  JSON_PATH_NEGATIVE_INDEX= 16
 };
 
 
@@ -93,7 +94,7 @@ typedef struct st_json_path_step_t
                                    /* see json_path_step_types */
   const uchar *key; /* Pointer to the beginning of the key. */
   const uchar *key_end;  /* Pointer to the end of the key. */
-  uint n_item;      /* Item number in an array. No meaning for the key step. */
+  int n_item;  /* Item number in an array. No meaning for the key step. */
 } json_path_step_t;
 
 
@@ -356,7 +357,7 @@ int json_skip_level_and_count(json_engine_t *j, int *n_items_skipped);
 */
 int json_find_path(json_engine_t *je,
                    json_path_t *p, json_path_step_t **p_cur_step,
-                   uint *array_counters);
+                   int *array_counters);
 
 
 typedef struct st_json_find_paths_t
@@ -365,7 +366,7 @@ typedef struct st_json_find_paths_t
   json_path_t *paths;
   uint cur_depth;
   uint *path_depths;
-  uint array_counters[JSON_DEPTH_LIMIT];
+  int array_counters[JSON_DEPTH_LIMIT];
 } json_find_paths_t;
 
 
@@ -425,13 +426,8 @@ int json_get_path_start(json_engine_t *je, CHARSET_INFO *i_cs,
 
 int json_get_path_next(json_engine_t *je, json_path_t *p);
 
-
-int json_path_parts_compare(
-        const json_path_step_t *a, const json_path_step_t *a_end,
-        const json_path_step_t *b, const json_path_step_t *b_end,
-        enum json_value_types vt);
 int json_path_compare(const json_path_t *a, const json_path_t *b,
-                      enum json_value_types vt);
+                      enum json_value_types vt, const int* array_size_counter);
 
 int json_valid(const char *js, size_t js_len, CHARSET_INFO *cs);
 
@@ -443,6 +439,8 @@ int json_locate_key(const char *js, const char *js_end,
 int json_normalize(DYNAMIC_STRING *result,
                    const char *s, size_t size, CHARSET_INFO *cs);
 
+int json_skip_array_and_count(json_engine_t *j, int* n_item);
+
 #ifdef  __cplusplus
 }
 #endif