Experimental support for Kitty image protocol in preview window

Close #3228

* Works inside and outside of tmux
* There is a problem where fzf unnecessarily displays the scroll offset
  indicator at the topbright of the screen when the image just fits the
  preview window. This is because `kitty icat` generates an extra line
  after the image area.

    # A 5-row images; an extra row at the end confuses fzf
    ["\e_Ga ... \e[9C􎻮̅̅ࠪ􎻮̅̍ࠪ􎻮̅̎ࠪ􎻮̅̐ࠪ􎻮̅̒ࠪ􎻮̅̽ࠪ􎻮̅̾ࠪ􎻮̅̿ࠪ􎻮̅͆ࠪ􎻮̅͊ࠪ􎻮̅͋ࠪ\n",
     "\r\e[9C􎻮̍̅ࠪ􎻮̍̍ࠪ􎻮̍̎ࠪ􎻮̍̐ࠪ􎻮̍̒ࠪ􎻮̍̽ࠪ􎻮̍̾ࠪ􎻮̍̿ࠪ􎻮̍͆ࠪ􎻮̍͊ࠪ􎻮̍͋ࠪ\n",
     "\r\e[9C􎻮̎̅ࠪ􎻮̎̍ࠪ􎻮̎̎ࠪ􎻮̎̐ࠪ􎻮̎̒ࠪ􎻮̎̽ࠪ􎻮̎̾ࠪ􎻮̎̿ࠪ􎻮̎͆ࠪ􎻮̎͊ࠪ􎻮̎͋ࠪ\n",
     "\r\e[9C􎻮̐̅ࠪ􎻮̐̍ࠪ􎻮̐̎ࠪ􎻮̐̐ࠪ􎻮̐̒ࠪ􎻮̐̽ࠪ􎻮̐̾ࠪ􎻮̐̿ࠪ􎻮̐͆ࠪ􎻮̐͊ࠪ􎻮̐͋ࠪ\n",
     "\r\e[9C􎻮̒̅ࠪ􎻮̒̍ࠪ􎻮̒̎ࠪ􎻮̒̐ࠪ􎻮̒̒ࠪ􎻮̒̽ࠪ􎻮̒̾ࠪ􎻮̒̿ࠪ􎻮̒͆ࠪ􎻮̒͊ࠪ􎻮̒͋ࠪ\n",
     "\r\e[39m\e8"]

* Example:

  fzf --preview='
    if file --mime-type {} | grep -qF 'image/'; then
      # --transfer-mode=memory is the fastest option but if you want fzf to be able
      # to redraw the image on terminal resize or on 'change-preview-window',
      # you need to use --transfer-mode=stream.
      kitty icat --clear --transfer-mode=memory --stdin=no --place=${FZF_PREVIEW_COLUMNS}x${FZF_PREVIEW_LINES}@0x0 {}
    else
      bat --color=always {}
    fi
  '

src/tui/light.go

@@ -31,6 +31,11 @@ const consoleDevice string = "/dev/tty"
 var offsetRegexp *regexp.Regexp = regexp.MustCompile("(.*)\x1b\\[([0-9]+);([0-9]+)R")
 var offsetRegexpBegin *regexp.Regexp = regexp.MustCompile("^\x1b\\[[0-9]+;[0-9]+R")
 
+func (r *LightRenderer) PassThrough(str string) {
+	r.queued.WriteString(str)
+	r.flush()
+}
+
 func (r *LightRenderer) stderr(str string) {
 	r.stderrInternal(str, true, "")
 }