show default value for BIT field in printable format


mysql-test/r/type_bit.result:
  Bug#35796 SHOW CREATE TABLE and default value for BIT field
  test result
mysql-test/t/type_bit.test:
  Bug#35796 SHOW CREATE TABLE and default value for BIT field
  test case
sql/item.cc:
  Bug#35796 SHOW CREATE TABLE and default value for BIT field
  issue an error if BIN|HEX deafult value is empty value
  (behaviour like for INT fields)