src/vs/base/browser/ui/scrollbar/scrollbarState.ts/ScrollbarState/getDesiredScrollPositionFromOffsetPaged
class ScrollbarState:	public getDesiredScrollPositionFromOffsetPaged(offset: number): number {
		if (!this._computedIsNeeded) {
			// no need for a slider
			return 0;
		}

		const correctedOffset = offset - this._arrowSize;  // compensate if has arrows
		let desiredScrollPosition = this._scrollPosition;
		if (correctedOffset < this._computedSliderPosition) {
			desiredScrollPosition -= this._visibleSize;  // page up/left
		} else {
			desiredScrollPosition += this._visibleSize;  // page down/right
		}
		return desiredScrollPosition;
	}