function getPointKey(astr) {
    return pointKeyMap[astr] || astr;
}
Appends values inside array attributes corresponding to given point number array
For use when pointData references a plot entity that arose (or potentially arose)
from multiple points in the input data

@param {object} pointData : point data object (gets mutated here)
@param {object} trace : full trace object
@param {Array(number)|Array(Array(number))} pointNumbers : Array of point numbers.
    Each entry in the array may itself be a length-2 array [row, col] to dig into 2D arrays