isLowercase function
Checks if the string is entirely lowercase.
A string is considered lowercase if it is unchanged when converted to lower case. Strings without cased characters (digits, symbols) and the empty string are considered lowercase.
Example:
isLowercase('hello'); // true
isLowercase('hello123'); // true
isLowercase('Hello'); // false
Implementation
bool isLowercase(String str) => _isLowercase(str);