padLeft method Null safety
Pads this string on the left if it is shorter than width.
Returns a new string that prepends padding onto this string
one time for each position the length is less than width.
const string = 'D';
print(string.padLeft(4)); // ' D'
print(string.padLeft(2, 'x')); // 'xD'
print(string.padLeft(4, 'y')); // 'yyyD'
print(string.padLeft(4, '>>')); // '>>>>>>D'
If width is already smaller than or equal to this.length,
no padding is added. A negative width is treated as zero.
If padding has length different from 1, the result will not
have length width. This may be useful for cases where the
padding is a longer string representing a single character, like
" " or "\u{10002}".
In that case, the user should make sure that this.length is
the correct measure of the string's length.
Implementation
String padLeft(int width, [String padding = ' ']);