input: def replace_all_occurrences(str: str, char: str, replacement: str) -> str:
      """Replace all occurrences of a character in a given string with the provided replacement character.
      >>> replace_all_occurrences("Hello World!", 'l', 'X')
      'HeXXo WorXd!'
      >>> replace_all_occurrences("the quick brown fox", 'o', 'a')
      'the quick brawn fax'
      """
output:     return str.replace(char, replacement)