Returns a matched substring from a regex handle. Substring ids start at 0 and end at captures-1, where captures is the number returned by Regex.Match or Regex.CaptureCount.
str_id = 0 is the full captured string, anything else is the capture group index. if Regex.Match is used match can only be 0
native bool GetSubString(int str_id, char[] buffer, int maxlen, int match = 0)