ui/vt100: Standardize on uint8_t for "ch" byte variables

The vt100 code is rather confused about how it handles bytes of data to be sent to the terminal: * vt100_input() takes a buffer of uint8_t * each byte is passed to vt100_putchar(), which takes "int ch" * that calls vt100_put_one(), which also takes "int ch" * vt100_put_one() sets TextCell::ch, which is uint8_t again * various places pass the TextCell:ch value to vt100_putcharxy(), which takes "int ch" again, but uses it unchecked as an index into a 256-entry array This confuses Coverity (e.g. CID 1659590) and the reader, who may be unsure whether the "int" variable really does hold only valid byte values 0..255 and whether we need to bounds-check before doing array dereferences. Standardize on keeping known-byte data in uint8_t all the way through. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com> Message-ID: <20260512104210.3330835-2-peter.maydell@linaro.org>