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".
The "report alternate keys" part of the Kitty keyboard protocol will
send an additional codepoint containing the "shifted" version of a
key based on the keyboard layout. This is useful for downstream
applications which set up keybindings based on symbols instead of
exact keys being pressed.
For example, underscore (_) with the Alt modifier is sent as minus (-)
with Alt and Shift modifiers. A terminal will send the underscore
codepoint as an alternate though, and we can use that information and
the presence of the Shift modifier to resolve the symbol. Other
examples are 'A-(' (sent as 'A-S-9') and 'A-)' (sent as 'A-S-0').
This change allows pushing the "report alternate keys" flag and
overwrites the keycode and modifiers for any shifted keys sent by the
terminal.
* Add a function for checking keyboard enhancement support
This follows the Kitty documentation's recommended way to check for
progressive keyboard enhancement: query the flags and then query the
primary device attributes (which is broadly supported). If we receive
only the device attributes, the protocol is not supported.
* Check keyboard enhancement in the event-read example
