Djot reader: add Space elements.

Previously we just got big Str elements with spaces included.
But many pandoc writers assume that breakable spaces will be
Space elements.  So, we got odd results with e.g. jira output.

Closes #11250.

src/Text/Pandoc/Readers/Djot.hs

@@ -186,7 +186,7 @@ convertInlines = fmap mconcat . mapM convertInline . F.toList . D.unMany
 convertInline :: PandocMonad m => D.Node D.Inline -> ReaderT Env m Inlines
 convertInline (D.Node pos attr il) = addAttrToInline pos attr <$>
   case il of
-    D.Str bs -> pure $ str (UTF8.toText bs)
+    D.Str bs -> pure $ text (UTF8.toText bs)
     D.Emph ils -> emph <$> convertInlines ils
     D.Strong ils -> strong <$> convertInlines ils
     D.Highlight ils -> spanWith ("",["mark"],[]) <$> convertInlines ils