This assumes the terminal uses UTF-8. If invalid UTF-8 is encountered (for
example because the terminal uses a legacy encoding), the code falls back
to the old method and feeds each byte as key code to the input code.
In theory, UTF-8 input could randomly fail, because the code in getch2.c
doesn't try to fill the input buffer correctly with input sequences
longer than a byte. This is a problem with the design of the existing
code.