Add an API function to calculate the UTF-8 encoded string length from Jerry string. (#1460)

JerryScript-DCO-1.0-Signed-off-by: Robert Sipka rsipka.uszeged@partner.samsung.com

docs/02.API-REFERENCE.md

@@ -1186,6 +1186,7 @@ jerry_get_utf8_string_size (const jerry_value_t value);
 **See also**
 
 - [jerry_create_string_from_utf8](#jerry_create_string_from_utf8)
+- [jerry_get_utf8_string_length](#jerry_get_utf8_string_length)
 
 ## jerry_get_string_length
 
@@ -1223,6 +1224,44 @@ jerry_get_string_length (const jerry_value_t value);
 - [jerry_create_string](#jerry_create_string)
 - [jerry_get_string_size](#jerry_get_string_size)
 
+## jerry_get_utf8_string_length
+
+**Summary**
+
+Get the length of an UTF-8 encoded string. Returns zero, if the value parameter is not a string.
+
+*Note*: The difference from [jerry_get_string_length](#jerry_get_string_length) is that it
+returns with utf-8 string length instead of the cesu-8 string length.
+
+**Prototype**
+
+```c
+jerry_length_t
+jerry_get_utf8_string_length (const jerry_value_t value);
+```
+
+- `value` - input string value
+- return value - number of characters in the string
+
+**Example**
+
+```c
+{
+  const jerry_char_t char_array[] = "a string";
+  jerry_value_t string = jerry_create_string_from_utf8 (char_array);
+
+  jerry_length_t string_length = jerry_get_utf8_string_length (string);
+
+  ... // usage of string_length
+
+  jerry_release_value (string);
+}
+```
+
+**See also**
+
+- [jerry_create_string_from_utf8](#jerry_create_string_from_utf8)
+- [jerry_get_utf8_string_size](#jerry_get_utf8_string_size)
 
 ## jerry_string_to_char_buffer