Converts all Unicode characters in the string that have a case to lowercase. The exact manner that this is done depends on the current locale, and may result in the number of characters in the string changing.
a UTF-8 encoded string
length of @str, in bytes, or -1 if @str is nul-terminated.
Return: a newly allocated string, with all characters converted to lowercase.
See Implementation
Converts all Unicode characters in the string that have a case to lowercase. The exact manner that this is done depends on the current locale, and may result in the number of characters in the string changing.