src/vs/editor/common/model/pieceTreeTextBuffer/pieceTreeBase.ts/PieceTreeBase/offsetInBuffer
class PieceTreeBase:	private offsetInBuffer(bufferIndex: number, cursor: BufferCursor): number {
		const lineStarts = this._buffers[bufferIndex].lineStarts;
		return lineStarts[cursor.line] + cursor.column;
	}