TextEditor: Remove "actionHack" and utilize contexts instead.

The actionHack was used to only forward actions to editors that "belong"
to that action handler instance. That is already clearly defined by the
context that the action handler is created for, so we can just use that
instead.

Change-Id: Ia4c6795c80bb281c1ed258324925f56ca7fd8150
Reviewed-by: Orgad Shaneh <orgads@gmail.com>