3643. Flip Square Submatrix Vertically

You are given an m x n integer matrix grid, and three integers x, y, and k. The integers x and y represent the row and column indices of the top-left corner of a square submatrix and the integer k represents the size (side length) of the square submatrix. Your task is to flip the submatrix by reversing the order of its rows vertically. Return the updated matrix. Example 1: Input: grid = [[1