function getParentFoldLine(lineNumber, foldingModel) {
    let startLineNumber = null;
    const foldingRegion = foldingModel.getRegionAtLine(lineNumber);
    if (foldingRegion !== null) {
        startLineNumber = foldingRegion.startLineNumber;
        // If current line is not the start of the current fold, go to top line of current fold. If not, go to parent fold
        if (lineNumber === startLineNumber) {
            const parentFoldingIdx = foldingRegion.parentIndex;
            if (parentFoldingIdx !== -1) {
                startLineNumber = foldingModel.regions.getStartLineNumber(parentFoldingIdx);
            }
            else {
                startLineNumber = null;
            }
        }
    }
    return startLineNumber;
}
Get line to go to for parent fold of current line
@param lineNumber the current line number
@param foldingModel the folding model

@return Parent fold start line