'driver': Widget binding: Use ${(k)widgets} instead of $(zle -la)

Avoids a fork.

Author: m0vie

zsh-syntax-highlighting.zsh

@@ -244,7 +244,7 @@ _zsh_highlight_bind_widgets()
 
   # Override ZLE widgets to make them invoke _zsh_highlight.
   local -U widgets_to_bind
-  widgets_to_bind=(${${(f)"$(builtin zle -la)"}:#(.*|orig-*|run-help|which-command|beep|set-local-history|yank)})
+  widgets_to_bind=(${${(k)widgets}:#(.*|orig-*|run-help|which-command|beep|set-local-history|yank)})
 
   # Always wrap special zle-line-finish widget. This is needed to decide if the
   # current line ends and special highlighting logic needs to be applied.