MDEV-18428 Memory: If transactional=0 is specified in CREATE TABLE, it is not possible to ALTER TABLE

* be strict in CREATE TABLE, just like in ALTER TABLE, because
  CREATE TABLE, just like ALTER TABLE, can be rolled back for any engine
* but don't auto-convert warnings into errors for engine warnings
  (handler::create) - this matches ALTER TABLE behavior
* and not when creating a default record, these errors are handled
  specially (and replaced with ER_INVALID_DEFAULT)
* always issue a Note when a non-unique key is truncated, because it's
  not a Warning that can be converted to an Error. Before this commit
  it was a Note for blobs and a Warning for all other data types.