StringSplit wrong behaviour when separator is empty

[hombreola]

According to the documentation in https://www.tensorflow.org/api_docs/python/tf/strings/split:

If sep is None or an empty string, consecutive whitespace are regarded as a single separator, and the result will contain no empty strings at the start or end if the string has leading or trailing whitespace.

However the current implementation performs a character by character split.

onnxruntime-extensions/operators/text/string_split.cc

Lines 36 to 50 in 98fb96d

	if (delimiter.size() == 0) {
	char word[2] = "a";
	for (int64_t row = 0; row < dimensions[0]; ++row) {
	const std::string& str = X[row];
	if (str.empty())
	continue;
	maxc = str.size() > maxc ? str.size() : maxc;
	for (auto it = str.begin(); it != str.end(); ++it) {
	word[0] = *it;
	words.push_back(word);
	indices.push_back(row);
	indices.push_back(std::distance(str.begin(), it));
	}
	}
	} else {

[wenbingl]

@xadupre , can you share some suggestion here?

[Evilmaax]

Any chance to address this issue in a future release?