Bring static functions into OutputDevice as private functions

Also rename them to something saner. ImplIsActionSpecial in particular
is not a particularly useful function name, so updating this for
clarity.

Functions renamed:
+ ImplIsActionHandlingTransparency() -> DoesActionHandleTransparency()
+ ImplIsActionSpecial() -> IsTransparentAction()

I've also updated some of the comments to clarify.

Change-Id: I6c9d0c33d96ce40af2c877b52da66de17ed8ce78