Switch from unmaintained paperclip to kt-paperclip (#16724)

* Switch from unmaintained paperclip to kt-paperclip

* Drop some compatibility monkey-patches not required by kt-paperclip

* Drop media spoof check monkey-patching

It's broken with kt-paperclip and hopefully it won't be needed anymore

* Fix regression introduced by paperclip 6.1.0

* Do not rely on pathname to call FastImage

* Add test for ogg vorbis file with cover art

* Add audio/vorbis to the accepted content-types

This seems erroneous as this would be the content-type for a vorbis stream
without an ogg container, but that's what the `marcel` gem outputs, so…

* Restore missing for_as_default method

* Refactor Attachmentable concern and delay Paperclip's content-type spoof check

Check for content-type spoofing *after* setting the extension ourselves, this
fixes a regression with kt-paperclip's validations being more strict than
paperclip 6.0.0 and rejecting some Pleroma uploads because of unknown
extensions.

* Please CodeClimate

* Add audio/vorbis to the unreliable set

It doesn't correspond to a file format and thus has no extension associated.

spec/models/media_attachment_spec.rb

@@ -114,6 +114,30 @@ RSpec.describe MediaAttachment, type: :model do
     end
   end
 
+  describe 'ogg with cover art' do
+    let(:media) { MediaAttachment.create(account: Fabricate(:account), file: attachment_fixture('boop.ogg')) }
+
+    it 'detects it as an audio file' do
+      expect(media.type).to eq 'audio'
+    end
+
+    it 'sets meta for the duration' do
+      expect(media.file.meta['original']['duration']).to be_within(0.05).of(0.235102)
+    end
+
+    it 'extracts thumbnail' do
+      expect(media.thumbnail.present?).to eq true
+    end
+
+    it 'extracts colors from thumbnail' do
+      expect(media.file.meta['colors']['background']).to eq '#3088d4'
+    end
+
+    it 'gives the file a random name' do
+      expect(media.file_file_name).to_not eq 'boop.ogg'
+    end
+  end
+
   describe 'jpeg' do
     let(:media) { MediaAttachment.create(account: Fabricate(:account), file: attachment_fixture('attachment.jpg')) }