Ensure Bit/ByteOrderChange parsers always exist at root
If the dfdl:byteOrder or dfdl:bitOrder properties were not provided,
Daffodil did not complain, and it would not insert a Bit/ByteOrderChange
parser at root. This meant that Daffodil would use a default value,
which in some cases caused incorrect behavior. It also meant that the
check for valid bit and byte orders (e.g. not bigEndian &
leastSignificantBitFirst) never occurred since that only happend in
ByteOrderChange parsers, meaning it could allow invalid bit/byte order
combinations.
This changes Daffodil so the root element will always insert Bit and
ByteOrderChange parsers, ensuring that the validity of the properties
are correct and ensuring correct parsing/unparsing. This means that
byteOrder is now always required, even in some cases where it might not
technically be needed.
This also modifies the initial UState/PState creation to not set
bit/byte order, but to instead rely on the Bit/ByteOrderChange parsers
to always be inserted first thing.
DFDL-1835
