terminal_image <-cwidth: code=int -> intNumber of columns the code point code occupies when drawn
in
terminal_image<-font:
0 for combining marks, 2 for wide characters and 1 for the rest. This is
the classification the renderer itself uses, so clients that must
predict our layout can share it rather than keep a second copy that
drifts. In particular it accounts for symbol and emoji code points that
the static Unicode tables call width 1 while an emoji-presenting font
draws them twice as wide. Fails while the terminal has no cell metrics
yet.
