[Arteims] AMQP 1.0 char type > 16 bits truncated

AMQP 1.0 uses UTF-32BE to encode its char type. However, Artemis appears to limit its char type size to 16 bits (perpaps UTF-16?), and instances of char > 16 bits are truncated.

For example, UTF-32 char 0x10ffff is truncated to 0xffff.