feat(fit-preview): optionally double comp_length when showing preview

When previews are enabled, they typically take up half the width of the
popup. This adds an option to make it double the width when preview is
enabled, hence ensuring that the full text of completion items are
visible.

lib/ftb-tmux-popup

@@ -45,6 +45,10 @@ local text REPLY comp_lines comp_length length popup_pad popup_min_size
 
 zstyle -a ":fzf-tab:$_ftb_curcontext" popup-pad popup_pad || popup_pad=(0 0)
 zstyle -a ":fzf-tab:$_ftb_curcontext" popup-min-size popup_min_size || popup_min_size=(0 0)
+zstyle -a ":fzf-tab:$_ftb_curcontext" popup-fit-preview popup_fit_preview_enabled || popup_fit_preview_enabled=no
+if [ "$popup_fit_preview_enabled" != "no" ] && zstyle -m ":fzf-tab:$_ftb_curcontext" fzf-preview '*'; then
+  popup_fit_preview=1
+fi
 
 # get the size of content, note we should remove all ANSI color code
 comp_lines=$(( ${#${(f)mapfile[$tmp_dir/completions.$$]}} + $popup_pad[2] ))
@@ -58,6 +62,11 @@ else
   # FIXME: can't get the correct width of CJK characters.
   comp_length=$( command perl -ne 's/\x1b\[[0-9;]*m//g;s/\x00//g; $m= length() if $m < length(); END { print $m }' < $tmp_dir/completions.$$ )
 fi
+
+if [ -n "$popup_fit_preview" ]; then
+  comp_length=$(( comp_length * 2 ))
+fi
+
 comp_length=$(( comp_length + $popup_pad[1] ))
 
 local popup_height popup_y popup_width popup_x adjust_height