Lua: add normalize function to *Pandoc* objects

This function performs a normalization of Pandoc documents. E.g.,
multiple successive spaces are collapsed, and tables are normalized such
that all rows and columns contain the same number of cells.

Closes: #10356

doc/lua-filters.md

@@ -1039,6 +1039,24 @@ equal in Lua if and only if they are equal in Haskell.
 `meta`
 :   document meta information ([Meta] object)
 
+### Methods {#type-pandoc-methods}
+
+#### normalize
+
+`normalize(self)`
+
+Perform a normalization of Pandoc documents. E.g., multiple
+successive spaces are collapsed, and tables are normalized, so
+that all rows and columns contain the same number of cells.
+
+Parameters:
+
+`self`
+:   the element ([Pandoc][])
+
+Results:
+
+-   cloned and normalized document. ([Pandoc][])
 
 ### walk {#type-pandoc:walk}
 

pandoc-lua-engine/test/lua/module/pandoc.lua

@@ -164,6 +164,13 @@ return {
       assert.are_same(meta.test, {pandoc.Plain{pandoc.Str 'check'}})
     end),
   },
+  group 'Pandoc' {
+    test('normalize', function ()
+      local doc = pandoc.Pandoc({{'a', pandoc.Space(), pandoc.Space(), 'b'}})
+      local normalized = pandoc.Pandoc({{'a', pandoc.Space(), 'b'}})
+      assert.are_equal(normalized, doc:normalize())
+    end),
+  },
   group 'Other types' {
     group 'ReaderOptions' {
       test('returns a userdata value', function ()