strlen() - return the number of UTF-8 characters in a supplied string

int strlen( string str );

strlen() returns the number of characters in the string 'str'.

LPC strings are UTF-8 encoded. Driver calcuate numbers of characters
according to the Unicode concept "Extended Grapheme Cluster", as defined in
"https://www.unicode.org/reports/tr29/".

strlen("abc") == 3
strlen("你好") == 2

sizeof(3)