* Share logic previously implemented for html/with formats through
a trait class
* source/bare formats doesn't execute a temporary redirect. the
JSON body will contain a key "redirect_target" instead if a wiki
redirect is found
* Introduce PageRedirectHandlerTest to test redirect logic shared
between multiple handlers
* Move Handler instatiation to HandlerTestTrait
* Update api-testing tests in Update.js
Change-Id: Id66e33e19adabdb3c9621eaea4a5d441f23edafd
This allows extensions like VisualEditor to safely instantiate REST
helper objects. It also reduces the number of services that need to be
injected into REST handlers from route definitions.
Change-Id: I10af85b2da96568cfffd03867d1cb299645fb371
