allCharFrequency function
Counts the frequency of all characters in the parameter string.
filterNonChars removes non-chars from count.
Implementation
Map<String, int> allCharFrequency(String str, {bool filterNonChars = true}) {
final out = <String, int>{};
for (final ch in str.split('')) {
if (filterNonChars && !ch.isChar) continue;
out.update(ch, (v) => v + 1, ifAbsent: () => 1);
}
return out;
}