This change both speeds up specs (less strings to allocate) and helps catch
cases where methods in Discourse are mutating inputs.
Overall we will be migrating everything to use #frozen_string_literal: true
it will take a while, but this is the first and safest move in this direction
Previously it would unhide their post but leave them silenced.
This fix also cleans up some of the helper classes to make it easier
to pass extra data to the silencing code (for example, a link to the
post that caused the user to be silenced.)
This patch also refactors the auto_silence specs to avoid using
stubs.
Sam Saffron
Robin Ward