It is possible to render images in terminals with protocols such as Sixel,
iTerm2's, or Kitty's. For a basic sixel or iTerm2 image printing, it is
sufficient to print some escape sequence with the data, e.g. cat image just
works, the image is displayed and enough lines are scrolled.
But for more sophisticated usage of images, such as TUIs, it is necessary to
know exactly what area that image would cover, in terms of columns/rows of
characters. Then it would be possible to e.g. resize the image to a size that
fits a col/row area precisely, not overdraw the image area, accommodate layouts,
etc.
Thus, provide the window size in pixel width/height, in addition to cols/rows.
The windows implementation always returns a "not implemented" error. The
windows API exposes a font-size, but in logical units, not pixels.
This could be further extended to expose either "logical window size",
or "pixel font size" and "logical font size".
