Given two numbers arr1 and arr2 in base -2, return the result of adding them together. Each number is given in array format:  as an array of 0s and 1s, from most significant bit to least significant bit.  For example, arr = [1,1,0,1] represents the number (-2)^3 + (-2)^2 + (-2)^0 = -3.  A number arr in array, format is also guaranteed to have no leading zeros: either arr == [0] or arr[0] == 1. Return the result of adding arr1 and arr2 in the same format: as an array of 0s and 1s with no leading zeros.