Fixed Katex standalone script (#6399)

Global macros are now persistent when using the HTML Writer with the --katex
option.

src/Text/Pandoc/Writers/HTML.hs

@@ -281,12 +281,14 @@ pandocToHtml opts (Pandoc meta blocks) = do
           H.script $ text $ T.unlines [
               "document.addEventListener(\"DOMContentLoaded\", function () {"
             , " var mathElements = document.getElementsByClassName(\"math\");"
+            , " var macros = [];"
             , " for (var i = 0; i < mathElements.length; i++) {"
             , "  var texText = mathElements[i].firstChild;"
             , "  if (mathElements[i].tagName == \"SPAN\") {"
             , "   katex.render(texText.data, mathElements[i], {"
             , "    displayMode: mathElements[i].classList.contains('display'),"
             , "    throwOnError: false,"
+            , "    macros: macros,"
             , "    fleqn: " <> katexFlushLeft
             , "   });"
             , "}}});"