Should be called in ascending order. Otherwise, call
lineCounter.lineStarts.sort() before calling linePos().
Performs a binary search and returns the 1-indexed { line, col }
position of offset. If line === 0, addNewLine has never been
called or offset is before the first known newline.
Tracks newlines during parsing in order to provide an efficient API for determining the one-indexed
{ line, col }position for any offset within the input.