concat method
Concatenate another spanned string with this one and return the result.
Touching spans with the same attribute will be merged.
Implementation
SpannedString concat(SpannedString other) {
return SpannedString.chars(
text + other.text,
other.spans
.shift(0, text.length)
.iter
.fold(spans, (ls, s) => ls.merge(s)),
);
}