Given a matrix of characters and an API Dictionary.isWord(String s), which return true/false.
Word can be formed only horizontally/vertically from the matrix not diagonally.
Return a list of valid words that can be formed from the matrix.
['a','b','c','d']
['t','p','q','x']
['a','m','a','t']
['d','a','c','d']
Your program should return ["am", "dam","cat"]
