indentation method
Calculates the length of indentation a String
has.
Implementation
// The behavior of tabs: https://spec.commonmark.org/0.30/#tabs
int indentation() {
var length = 0;
for (final char in codeUnits) {
if (char != $space && char != $tab) {
break;
}
length += char == $tab ? 4 - (length % 4) : 1;
}
return length;
}