check-qjson: Test noncharacters other than U+FFFE, U+FFFF in strings

Test cases cover the two noncharacters in the BMP.  Add tests for the
other 64 noncharacters.

Three existing test cases involve noncharacters U+FFFF and U+10FFFF.
Instead of deleting them as now duplicates, adjust them to use U+FFFC
and U+10FFFFD.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
