input: Write a function to replace all occurrences of a given character in a string with the provided replacement character. If the character is not found in the string, return the original string without any changes. The function should take the original string, the character to be replaced, and the replacement character as parameters.
  assert replace_all_occurrences("Hello World!", 'l', 'X')=="HeXXo WorXd!"
  assert replace_all_occurrences("Python Programming", 'o', 'Y')=="PYthYn PrYgramming"
  assert replace_all_occurrences("No changes needed", 'X', 'Y')=="No changes needed"
  assert replace_all_occurrences("", 'a', 'b')==""
  assert replace_all_occurrences("A.", '.', '!')=="A!"
output: def replace_all_occurrences(original_string, char_to_replace, replacement_char):
      return original_string.replace(char_to_replace, replacement_char)