fix garmin serial/usb device character encoding/decoding. (#1117)

fix garmin serial/usb device character encoding/decoding. (#1117)

* attempt to use correct codec with garmin reader.

the garmin writer is unchanged as of yet.

* fix garmin writer wrt encoding.

* add garmin option to force codec.

* update serialization ref files for garmin codec option.

* fix potential overwrite bug with route/track names

in garmin writer.

* fix up for old Qt.

* correct assertion

* use static_assert to for fixed buffer size checks.

* document garmin codec option

* don't clean rtept/trkpt names for newer devices.

We clear badchars for newer devices already, effectively not
cleaning wpt names.