src/vs/editor/common/services/editorSimpleWorker.ts/MirrorModel/positionAt
class MirrorModel:	public positionAt(offset: number): IPosition {
		offset = Math.floor(offset);
		offset = Math.max(0, offset);

		this._ensureLineStarts();
		const out = this._lineStarts!.getIndexOf(offset);
		const lineLength = this._lines[out.index].length;

		// Ensure we return a valid position
		return {
			lineNumber: 1 + out.index,
			column: 1 + Math.min(out.remainder, lineLength)
		};
	}