Revert "wrapping: Don't add '--' when invoking widgets."

The '--' guard was correct; it was there to guard against arguments belonging
to the syntax «zle widget [ -n num ] [ -Nw ] [ -K keymap ] args».

For example, this affected using <backward-kill-word> over
    BUFFER="-w "
    CURSOR=3
after
    autoload -Uz select-word-style
    select-word-style default
    zstyle ':zle:backward-kill-word' word-style shell
.

This reverts commit c808d2187a.

zsh-syntax-highlighting.zsh

@@ -208,16 +208,16 @@ _zsh_highlight_bind_widgets()
 
       # User defined widget: override and rebind old one with prefix "orig-".
       user:*) eval "zle -N orig-$cur_widget ${widgets[$cur_widget]#*:}; \
-                    _zsh_highlight_widget_$cur_widget() { _zsh_highlight_call_widget orig-$cur_widget \"\$@\" }; \
+                    _zsh_highlight_widget_$cur_widget() { _zsh_highlight_call_widget orig-$cur_widget -- \"\$@\" }; \
                     zle -N $cur_widget _zsh_highlight_widget_$cur_widget";;
 
       # Completion widget: override and rebind old one with prefix "orig-".
       completion:*) eval "zle -C orig-$cur_widget ${${widgets[$cur_widget]#*:}/:/ }; \
-                          _zsh_highlight_widget_$cur_widget() { _zsh_highlight_call_widget orig-$cur_widget \"\$@\" }; \
+                          _zsh_highlight_widget_$cur_widget() { _zsh_highlight_call_widget orig-$cur_widget -- \"\$@\" }; \
                           zle -N $cur_widget _zsh_highlight_widget_$cur_widget";;
 
       # Builtin widget: override and make it call the builtin ".widget".
-      builtin) eval "_zsh_highlight_widget_$cur_widget() { _zsh_highlight_call_widget .$cur_widget \"\$@\" }; \
+      builtin) eval "_zsh_highlight_widget_$cur_widget() { _zsh_highlight_call_widget .$cur_widget -- \"\$@\" }; \
                      zle -N $cur_widget _zsh_highlight_widget_$cur_widget";;
 
       # Default: unhandled case.