input: Write a function to replace all occurrences of a given character in a string with the provided replacement character. If the input string is empty, return the empty string.
  assert replace_all_occurrences("Hello World!", 'l', 'X') == 'HeXXo WorXd!'
  assert replace_all_occurrences("abracadabra", 'a', 'z') == 'zbrzczdzbrz'
  assert replace_all_occurrences("", 'x', 'y') == ""
  assert replace_all_occurrences("xxxxx", 'x', 'y') == "yyyyy"
  assert replace_all_occurrences("abc", 'd', 'e') == "abc"
output: def replace_all_occurrences(s, char, replacement):
      return s.replace(char, replacement)