Test suite: Start testing our output for valid UTF-8.

Feed the output of `tshark -G <glossary>` to `iconv -f UTF-8`. Adjust a
couple of the Bluetooth dissectors and X11 keysyms accordingly.

Change-Id: I5b04dc3fa4734c8f0a795daf44bd398fe5ebc1bd
Reviewed-on: https://code.wireshark.org/review/6147
Reviewed-by: Gerald Combs <gerald@wireshark.org>
(cherry picked from commit dfa49cdd1653493456d7188950c4c66917c66572)
Conflicts:
	epan/dissectors/packet-bthci_evt.c
	test/suite-clopts.sh
Reviewed-on: https://code.wireshark.org/review/6148