Show module doc with the correct direction formatting

* Add mw-content-(ltr|ltr) class to the documentation <div>.
* Rewrite the div code as Html::rawElement instead of
  concatenating a string.

Done in pairing with Niklas Laxström.

Change-Id: I4d68d53df9dcf3556885552b738f2c327aaa8607
Merge "Show module doc with the correct direction formatting"