feat: add RTL Support and update demo site to Show Arabic/RTL content (#519)

* add LanguageDirection variable

* add .direction-rtl and .direction-ltr clases

* margin -right > margin-inline-end

* keep Codeblocks LTR

* switch to logical properties

* left -> inset-inline-start

* Add Arabic/RTL placeholder text

* Add arabic language

* remove space

* use Html Dir instead of class

* Move codeblock code to layout/article.css and fix 4 spaces codeblocks

* remove unused clases

exampleSite/config.yaml

@@ -13,6 +13,11 @@ languages:
         languageName: 中文
         title: 演示站点
         weight: 2
+    ar:
+        languageName: عربي
+        languagedirection: rtl
+        title: موقع تجريبي
+        weight: 3
 
 # Change it to your Disqus shortname before using
 disqusShortname: hugo-theme-stack
@@ -21,7 +26,7 @@ disqusShortname: hugo-theme-stack
 googleAnalytics:
 
 # Theme i18n support
-# Available values: en, fr, id, ja, ko, pt-br, zh-cn, zh-tw, es, de, nl, it, th, el, uk
+# Available values: en, fr, id, ja, ko, pt-br, zh-cn, zh-tw, es, de, nl, it, th, el, uk, ar
 DefaultContentLanguage: en
 
 # Set hasCJKLanguage to true if DefaultContentLanguage is in [zh-cn ja ko]