contains method
Checks if the string contains other.
caseSensitive determines whether the search is case-sensitive (default: true).
Example:
final name = react('Flutter');
name.contains('flut', caseSensitive: false); // true
Implementation
bool contains(String other, {bool caseSensitive = true}) {
final v = caseSensitive ? value : value.toLowerCase();
final t = caseSensitive ? other : other.toLowerCase();
return v.contains(t);
}