Fix process of receiving posts with bearcaps is not working

[kmycode]

Currently, Mastodon is unable to receive post with Bearcaps from ActivityPub.
Originally @object['content'] should be used as the status text, but @json['content'] is currently used.

First, received json is saved to @json and @object.

  # activity.rb
  def initialize(json, account, **options)
    @json    = json
    @account = account
    @object  = @json['object']
    @options = options
  end

@json <= Received json
@object <= Received json

Next, the program reads the signature post and sets the data in the @object.

  # activity.rb
  def dereference_object!
    return unless @object.is_a?(String)

    dereferencer = ActivityPub::Dereferencer.new(@object, permitted_origin: @account.uri, signature_actor: signed_fetch_actor)

    @object = dereferencer.object unless dereferencer.object.nil?
  end

@json <= Received json
@object <= Dereferenced json

Finally, StatusParser uses data from @json.

  # create.rb
  def process_status_params
    @status_parser = ActivityPub::Parser::StatusParser.new(@json, followers_collection: @account.followers_url)

Therefore, @json['content'] is read as status text.
This is fine for normal posts, but an empty string is always returned for signed posts (Bearcaps posts).

I fixed calling StatusParser.new on this pull request.

[noellabo]

@Gargron @ClearlyClaire This bug made it incompatible with Fedibird's circles feature (yes, it's a remnant of a previously unmerged Mastodon feature). Could you please merge this PR into v4.2?

[ClearlyClaire]

Sorry it slipped through. I'm not confident in having it in 4.2.0, which is scheduled for today, but I will try to have a deeper look at it in the near future, to have it in 4.3.0 and possibly in a backport for 4.2 and 4.1

[noellabo]

Please merge this fix into the v4.3 release.
For a long time, servers using Bearcaps have been having trouble communicating with Mastodon.
@ClearlyClaire

[ClearlyClaire]

Sorry I forgot about this again!

Looks good to me, I'll add tests in a follow-up PR.