You are given a Google Doc like this one that contains a list of Unicode characters and their positions in a 2D grid. Your task is to write a function that takes in the URL for such a Google Doc as an argument, retrieves and parses the data in the document, and prints the grid of characters. When printed in a fixed-width font, the characters in the grid will form a graphic showing a sequence of uppercase letters, which is the secret message.
The document specifies the Unicode characters in the grid, along with the x- and y-coordinates of each character.
The minimum possible value of these coordinates is 0. There is no maximum possible value, so the grid can be arbitrarily large.
Any positions in the grid that do not have a specified character should be filled with a space character.