src/vs/editor/browser/controller/textAreaState.ts/TextAreaState/_finishDeduceEditorPosition
class TextAreaState:	private _finishDeduceEditorPosition(anchor: Position | null, deltaText: string, signum: number): [Position | null, number, number] {
		let lineFeedCnt = 0;
		let lastLineFeedIndex = -1;
		while ((lastLineFeedIndex = deltaText.indexOf('\n', lastLineFeedIndex + 1)) !== -1) {
			lineFeedCnt++;
		}
		return [anchor, signum * deltaText.length, lineFeedCnt];
	}