Make some filters use 'topdown' traversal

It allows to stop the traversal early, which is particularly useful when
using `jog`.

Author: tarleb

src/resources/filters/normalize/normalize.lua

@@ -22,15 +22,16 @@ local shortcode_ast = require 'modules/astshortcode'
 
 local function stripNotes(el) 
   local result = _quarto.ast.walk(el, {
-    Note = function(_el)
-      return pandoc.Null()
+    Note = function()
+      return {}
     end
   })
   return result
 end
 
 function normalize_filter() 
   return {
+    traverse = 'topdown',
     Meta = function(meta)
       -- normalizes the author/affiliation metadata
       local normalized = authors.processAuthorMeta(meta) or meta
@@ -65,15 +66,15 @@ function normalize_filter()
       -- since that will result in duplicate footnotes
       -- in the rendered output
       if div.classes:includes('hidden') then
-        return stripNotes(div)
+        return stripNotes(div), false
       end
     end,
     Span = function(span)
       -- Don't allow footnotes in the hidden element (markdown pipeline)
       -- since that will result in duplicate footnotes
-      -- in the rendered output      
+      -- in the rendered output
       if span.classes:includes('hidden') then
-        return stripNotes(span)
+        return stripNotes(span), false
       end
     end
   }