function* mapEscapeSequenceOrLineContinuation(reader) {
	const start = reader.pos;
	const str = readEscapeSequenceOrLineContinuation(reader);
	const end = reader.pos;
	const source = reader.source.slice(start, end);

	switch (str.length) {
		case 0:
			break;
		case 1:
			yield new CodeUnit(start, source);
			break;
		default:
			yield new CodeUnit(start, source);
			yield new CodeUnit(start, source);
			break;
	}
}
Reads an escape sequence or line continuation and generates the respective `CodeUnit` elements.
@param {TextReader} reader The reader should be positioned on the backslash.
@returns {Generator<CodeUnit>} Zero, one or two `CodeUnit` elements.