fix(form-builder): point slug focus to current field

When the slug field was focused, it used the current (root) path for the focus path,
which prevented the input from actually opening inside of arrays, as well as presence
indication not showing up over the field.

Fixes #2379.

packages/@sanity/form-builder/src/inputs/Slug/SlugInput.tsx

@@ -100,7 +100,7 @@ const SlugInput = React.forwardRef(function SlugInput(
     updateSlug,
   ])
 
-  const handleFocus = React.useCallback(() => onFocus(), [onFocus])
+  const handleFocus = React.useCallback(() => onFocus(['current']), [onFocus])
 
   return (
     <ChangeIndicatorCompareValueProvider