feat (theme): isRTL, allow tests on tags other than html

Author: n-langle

src/js/utils/isRTL.js

@@ -1,7 +1,3 @@
-export default function isRTL() {
-  return (
-    document.documentElement.dir === 'rtl' ||
-    document.documentElement.lang === 'ar' ||
-    document.documentElement.lang === 'iw'
-  )
+export default function isRTL(container = document.documentElement) {
+  return container.dir === 'rtl' || ['ar', 'iw'].includes(container.lang)
 }