src/vs/editor/contrib/folding/browser/foldingRanges.ts/FoldingRegions/setCollapsed
class FoldingRegions:	public setCollapsed(index: number, newState: boolean) {
		let arrayIndex = (index / 32) | 0;
		let bit = index % 32;
		let value = this._collapseStates[arrayIndex];
		if (newState) {
			this._collapseStates[arrayIndex] = value | (1 << bit);
		} else {
			this._collapseStates[arrayIndex] = value & ~(1 << bit);
		}
	}