Implement our own grapheme measuring function which switches on whether
the terminal supports mode 2027
Signed-off-by: Tim Culverhouse <tim@timculverhouse.com>
We use two screens: one which the user provides a slice of bytes for the
graphemes, and the user owns the bytes. We copy those bytes to our
internal model so that we can compare between frames
Signed-off-by: Tim Culverhouse <tim@timculverhouse.com>
