symbolExists function
Whether an FSW symbol key corresponds to an existing ISWA glyph
(width > 0 && height > 0). Malformed keys return false.
Mirrors the _symbol_exists helper used by Python's mirror module.
Implementation
bool symbolExists(String symbol) {
try {
final size = getSymbolSize(symbol);
return size.item1 > 0 && size.item2 > 0;
} on FormatException {
return false;
}
}