(Experimental) Add support for iTerm2 inline image protocol

Close #1102

  fzf --preview 'imgcat -W $FZF_PREVIEW_COLUMNS -H $FZF_PREVIEW_LINES {}'

Notes:
* There is no good way to determine the height of the rendered image,
  so we assume that the image takes the full height of the preview
  window. So the image cannot be displayed with the other text.
* fzf-preview.sh script was updated to use `imgcat` if it's available
  but `chafa` is not.
* iTerm2 also supports Sixel, so adding support for this protocol is not
  quite necessary but it renders animated GIFs much better (e.g. looping).

bin/fzf-preview.sh

@@ -4,8 +4,9 @@
 # image in the preview window of fzf.
 #
 # Dependencies:
-# - https://github.com/hpjansson/chafa
 # - https://github.com/sharkdp/bat
+# - https://github.com/hpjansson/chafa
+# - https://iterm2.com/utilities/imgcat
 
 if [[ $# -ne 1 ]]; then
   >&2 echo "usage: $0 FILENAME"
@@ -44,6 +45,7 @@ elif ! [[ $KITTY_WINDOW_ID ]] && (( FZF_PREVIEW_TOP + FZF_PREVIEW_LINES == $(stt
   dim=${FZF_PREVIEW_COLUMNS}x$((FZF_PREVIEW_LINES - 1))
 fi
 
+# 1. Use kitty icat on kitty terminal
 if [[ $KITTY_WINDOW_ID ]]; then
   # 1. 'memory' is the fastest option but if you want the image to be scrollable,
   #    you have to use 'stream'.
@@ -52,10 +54,21 @@ if [[ $KITTY_WINDOW_ID ]]; then
   #    This confuses fzf and makes it render scroll offset indicator.
   #    So we remove the last line and append the reset code to its previous line.
   kitty icat --clear --transfer-mode=memory --stdin=no --place="$dim@0x0" "$file" | sed '$d' | sed $'$s/$/\e[m/'
+
+# 2. Use chafa with Sixel output
 elif command -v chafa > /dev/null; then
   chafa -f sixel -s "$dim" "$file"
   # Add a new line character so that fzf can display multiple images in the preview window
   echo
+
+# 3. If chafa is not found but imgcat is available, use it on iTerm2
+elif command -v imgcat > /dev/null; then
+  # NOTE: We should use https://iterm2.com/utilities/it2check to check if the
+  # user is running iTerm2. But for the sake of simplicty, we just assume
+  # that's the case here.
+  imgcat -W "${dim%%x*}" -H "${dim##*x}" "$file"
+
+# 4. Cannot find any suitable method to preview the image
 else
   file "$file"
 fi