src/vs/editor/contrib/folding/hiddenRangeModel.ts/findRange
function findRange(ranges: IRange[], line: number): IRange | null {
	let i = findFirstInSorted(ranges, r => line < r.startLineNumber) - 1;
	if (i >= 0 && ranges[i].endLineNumber >= line) {
		return ranges[i];
	}
	return null;
}