Don't require hook subscribers to know language direction

Allows extensions to pass the screenshot image as an array with
'ltr' and 'rtl' keys if the image differs across layouts.

This will prevent some of the recursion that occurs when calling
->getLanguage() on RequestContext::getMain().

Bug: 62124
Change-Id: I1c72aaa3f847b1b7679113f2b88cbb92adf0f936
Merge "Don't require hook subscribers to know language direction"