`context` fields for objects and activities can now be generated based
on the object/activity `inReplyTo` field or its ActivityPub ID, as a
fallback method in cases where `context` fields are missing for incoming
activities and objects.
When no image description is filled in, Pleroma allowed fallbacks.
Those were (based on a setting) either the filename, or a fixed description.
Neither are good options for image descriptions imo, so here we remove this.
Note that there's two tests removed who supposedly tested something else.
But examining closer, they didn't seem to test what they claimed to test,
so I removed them rather than try to "fix" them.
Objects who got updated would just pass through several of the MRF policies, undoing moderation in some situations.
In the relevant cases we now check not only for Create activities, but also Update activities.
I checked which ones checked explicitly on type Create using `grep '"type" => "Create"' lib/pleroma/web/activity_pub/mrf/*`.
The following from that list have not been changed:
* lib/pleroma/web/activity_pub/mrf/follow_bot_policy.ex
* Not relevant for moderation
* lib/pleroma/web/activity_pub/mrf/keyword_policy.ex
* Already had a test for Update
* lib/pleroma/web/activity_pub/mrf/object_age_policy.ex
* In practice only relevant when fetching old objects (e.g. through Like or Announce). These are always wrapped in a Create.
* lib/pleroma/web/activity_pub/mrf/reject_non_public.ex
* We don't allow changing scope with Update, so not relevant here
Objects who got updated would just pass the TagPolicy, undoing the moderation that was set in place for the Actor.
Now we check not only for Create activities, but also Update activities.
This fixes a race condition bug where keys could be regenerated
post-federation, causing activities and HTTP signatures from an user to
be dropped due to key differences.
Non-Create/Listen activities had their associated object field
normalized and fetched, but only to use their `id` field, which is both
slow and redundant. This also failed on Undo activities, which delete
the associated object/activity in database.
Undo activities will now render properly and database loads should
improve ever so slightly.
